Method and apparatus for alignment, comparison & identification of characteristic tool marks, including ballistic signatures

[0001] This application is a continuation of, and claims priority from, U.S. patent application Ser. No. 09/329,217, filed Jun. 10, 1999, now U.S. Pat. No. 7,068,808 of the same title, which in turn claims priority from U.S. Provisional Patent Application No. 60/087,512 filed Jun. 10, 1998.

[0002] The method and apparatus of this patent involve tool mark identification, which is a type of forensic analysis aimed at comparing images of marks made on an item with images of marks stored in a database to find any which appear similar enough that they could have been made by the same tool. The principal purpose is to find linkage between items associated with crimes, to assist in solving the crimes. The primary application is for analysis of ballistic items, which includes guns, bullets, and shell casings.

[0003] Guns, including pistols, revolvers, semiautomatics, rifles, and shotguns are used in the commission of thousands of crimes per day throughout the country. There is growing interest in tracing the source and movement of guns. Often crimes are solved by being able to associate one crime with another, or a crime with a particular gun, or a gun with a particular person. Tools used during commission of a crime often leave characteristic marks at the crime scene, which marks can be useful in linking together various crimes, or in linking a crime to a weapon, or in linking a crime to a criminal. The evidence that allows such links to be developed involves particular tool marks, which each weapon makes on the bullets and shell casings fired from it.

[0004] Because the evidence must be protected against contamination and the chain of custody must be preserved, and since it is often desirable to compare markings obtained at one crime scene to those obtained at others, it has become common to create images of the markings and use computer systems for automated comparison of the images from newly obtained specimens with databases of previously obtained images. Only after a possible match has been determined are the physical specimens viewed side by side.

[0005] Ammunition for handguns, rifles and shotguns all contain an outer casing or shell, a primer device to ignite, a fast burning material which is a form of nitrocellulose, and a projectile to fly out the barrel. Ammunition that travels through a particular gun receives scratches from the barrel of the gun, indentation from the firing pin, and perhaps other marks from the breech face and ejector. These tool marks are characteristic of the particular weapon used, and may be used to link a bullet or casing with the weapon from which they were fired.

[0006] The shell casing receives marking from the firing pin hitting the primer, from the back pressure of the gas expansion forcing the casing against the breech face of the firing pin housing which may have marks or defects which transfer onto the primer and/or casing. These marks may be a result of manufacturing defects, or hand finishing done in high quality weapons. Breech face marks can be compared just as can firing pin marks, either by firing a test round or by examining the weapon when the weapon is available, or by comparing corresponding marks on two bullets or casings which are suspected of coming from the same weapon. If the same weapon is used to fire the same type ammunition at the same type target from the same distance, comparable patterns will be produced on the bullet and casing. If the ammunition is changed, the patterns will be somewhat different.

[0007] Tool marks can be also transferred to the casing by the extractor and ejector of semiautomatics and automatics. Such marks include indentations and striations. The ejector is likely to gouge the casing. The extractor pulls the casing from the breech, imposing perhaps additional striations and indents before it hits the ejector.

[0008] Class characteristic marks vary with calibre, load, material used for the bullet or shot, bullet weight, its impact behavior, material used for the casing, and identification stamped into the bullet and casing. Intentional marks on ammunition include information stamped on the face of the bullet casing during molding of the shells. Some casings and bullets also have an indented ring or rings around the circumference called a canellure. These are smeared with grease or wax as sealer, making the bullet water-resistant and providing some lubrication as it is forced through the barrel. The canellures on the casing are imprinted within a quarter inch from the top after the bullet is inserted. This crimp acts to seal the round and hold the bullet in the casing. Canellures may contain imprint information unique to the manufacturer and perhaps to a particular crimping tool.

[0009] Ammunition for handguns, rifles and shotguns all contain an outer casing or shell, a primer device to ignite, a fast burning material which is a form of nitrocellulose, and a projectile to fly out the barrel. Ammunition that travels through a particular gun receives scratches from the barrel of the gun, indentation from the firing pin, and perhaps other marks from the breech face and ejector, in addition to fingerprints. The hand of the person firing the weapon receives a spray of gun residue which may be characteristic of a particular type of weapon and ammunition. The target receives some degree of blowback from the weapon and the target itself, plus perhaps fragments of any materials through which the bullet passed.

[0010] Markings on ballistic items which are of interest to forensics include:

• • [0011] Fingerprints on the weapon, projectile, or casing.
  • [0012] Other debris and material on the weapon, projectile, or casing.
  • [0013] Characteristics on the projectile or casing associated with the particular brand and type of ammunition used.
  • [0014] Characteristics on the projectile or casing associated with the particular weapon used. These are called tool marks.

[0015] During manufacture, grooves are cut into the hard steel of pistol and rifle barrels, spiraling from the chamber to the muzzle. They cause the bullet to spin, which results in the bullet having a cleaner trajectory and the weapon having more accurate targeting. The raised areas between grooves are called lands. Bullets are intended to be fired in a particular calibre weapon. Nitrocellulose burns to produce an expanding gas, which drives the bullet through the barrel. The resulting heat causes the bullet to expand and softens its surface. Lead bullets are particularly prone to softening. The bullet is blown out of the shell casing and forced into the barrel, which is tighter. As a result, the lands are cut into the moving bullet and the surface is squeezed into the grooves. The high points of the barrel cause scratches in the bullet, which are referred to as striation evidence. The material used in the bullet determines the depth of the striations.

[0016] The number, width and depth of the grooves and the angle and direction (right or left) of their spiral are determined by the manufacturer. Lands and grooves together are called rifling. Rifling marks are transferred to the bullet as it is forced through the barrel. Some marks indicate the class of weapon used, while others indicate the particular gun or barrel used in the case of weapons with interchangeable barrels.

[0017] Most weapons other than Colt use a right twist. The number of lands or grooves typically is four to seven. The width varies depending on the number and the calibre. The degree of twist is measured by the distance traveled during one complete rotation of the bullet. A typical Colt handgun can be described as a left twist, six lands, 1/12. Most handgun barrels are shorter than 12 inches. Therefore, the energy transferred to spinning the bullet is not as great as in a rifle.

[0018] When the ammunition used is smaller than that designed to be used in a weapon, the result is loss of energy and penetration. In addition, since the bullet is loose within the barrel, inconsistent striations will occur on various bullets fired through the weapon.

[0019] Maintenance done on a weapon can alter the characteristics imposed on its ammunition. Use, cleaning, corrosion, and intentional damage to a barrel can all affect the ability to match ammunition used in it over time. Rust or corrosion will alter fine details. Some semiautomatics and automatics have interchangeable barrels. After exiting the barrel, the bullet may receive additional distortions as it passes through various materials. The result may be to destroy the forensic value of the bullet, or may be just to require further analysis.

[0020] The shell casing receives marking from the firing pin hitting the primer, from the back pressure of the gas expansion slamming the casing against the breech face of the firing pin housing which may have marks or defects which transfer onto the primer and/or casing. These marks may be a result of manufacturing defects, or result from the hand finishing done in high quality weapons. Breech face marks can be compared just as can firing pin marks, either by firing a test round or by examining the weapon when the weapon is available, or by comparing corresponding marks on two bullets or casings which are suspected of coming from the same weapon. If the same weapon is used to fire the same type ammunition at the same type target from the same distance, comparable patterns will be produced on the bullet and casing. If the ammunition is changed, the patterns will be different.

[0021] Shell casings are ejected immediately from automatic and semis, and so fall close to where the firing occurs. Revolvers retain the casings until intentionally ejected, and so are often carried away from the crime scene. Tool marks can be transferred to the casing by the extractor and ejector of semis and automatics. Such marks include indentations and striations. The ejector is likely to gouge the casing. The extractor pulls the casing from the breech, imposing perhaps additional striations and indents before it hits the ejector.

[0022] Class characteristic marks vary with calibre, load, material used for the bullet or shot, bullet weight, its impact behavior, material used for the casing, and identification stamped into the bullet and casing. Intentional marks on ammunition include information stamped on the face of the bullet casing during molding of the shells. Some casings and bullets, particularly lead, also have an indented ring or multiple rings around the circumference called a canellure. These are smeared with grease or wax when first inserted into the casing. The material acts as sealer, making the bullet water-resistant and providing some lubrication as it is forced through the barrel. The canellures on the casing are imprinted within a quarter inch from the top after the bullet is inserted. This crimp acts to further seal the round and hold the bullet in the casing. Canellures may contain imprint information unique to the manufacturer and perhaps even to a particular crimping tool.

[0023] Types of ammunition are distinguished by their size. All handguns are designated by calibre in either inches or millimeters. For example a .22 calibre is 22/100 inch. The length of the shell varies to increase the capacity of gunpowder. A 0.22 may be short, long or long rifle, plus a magnum load. All magnum loads contain more gunpowder and may propel a heavier bullet. Magnum weapons are always designed to be heavier to contain the increased force. A magnum weapon can chamber a regular load, but a regular weapon cannot chamber a magnum round.

[0024] Some 0.22 handguns and rifles can chamber only the short, some can chamber short and long, and others can handle all three. The 0.22 short and long have the same weight bullet, while the long has more powder. The long rifle has more powder still and a heavier bullet but still is not considered a magnum load. All .22 rounds of these types are rim fire primers, rather than center core primers. Some high-powered rifles can proper .22 calibre bullets with center core primers, but the shell casings are huge relative to this group.

[0025] The .25 calibre pistol purse gun is designed to be easily concealed. There are .32 calibre revolvers and semiautomatics. The .32 calibre rim fire primers were used in early revolvers, but all modern rounds are center core primers.

[0026] There are two types of ammunition for .38 calibre (.357) revolvers; the .38 S&W and the .38 Special. The .38 Smith and Wesson is a shorter shell with smaller load. It has been superceded by the more powerful .38 Special, designed for law enforcement use. The maximum stopping power for the .38 calibre became available when the .357 magnum was marketed. The weapon fires a heavier bullet, with longer casing that contains additional gunpowder. However, when firing a solid lead bullet, the weapon proved a hazard to unintended secondary targets, because the penetrating power was too great.

[0027] For police use, a combination of stopping power and safety are desired. Several .38 calibre bullets are designed to impact only the first target, transferring all the kinetic energy to it. Hollow point bullets were designed for this purpose. A hollow point is a soft lead bullet encased in a thin steel jacket. The point is actually an opening with thin lead walls. On impact the wall flare out. The final shape of the bullet, in the side view is similar to a mushroom. Hence the term “mushrooming” is applied. Hollow points don't necessarily mushroom every time, and can still harm secondary targets, such as by passing through soft tissue of the target and injuring someone behind.

[0028] Glasser bullets were developed with a prefragmented round constructed of a thin metal skin packed with very small lead particles suspended in liquid Teflon. The bullet's weight is equal to that of a solid lead bullet, resulting in equivalent kinetic energy. When the Glasser hits any resisting surface, the thin walls flatten out, distributing the tiny lead particles over a wide area. A bullet hitting a human or animal penetrates and opens up, transferring all its energy to the inside of the target, having an elephant gun effect. The Glasser offered improved safety since all energy was expended when the bullet hit something. Errant shots striking pavement would not ricochet. Bullets hitting a house would not penetrate walls. Other manufacturers also offer prefragmented bullets.

[0029] Shotgun shells are different from handgun and rifle ammunition. Although solid metal casings have been used, they are now mostly replaced by a combination casing with a metal face and base connected to a plastic or waxed cardboard cylinder. Shotgun shells are available in gauges 10, 12, 14, 16, 20, and 410. The cylinder is crimped shut, sealing in the projectiles, shot and other materials with the gunpowder. The face contains manufacturer's information and markings and houses a center core primer. The actual projectiles vary. The shot, which was traditionally lead, is gradually being replaced by steel balls. Lead shot has been cited by environmentalists as causing lead contamination in waterways.

[0030] Firearms examiners can study the shell casings collected at one crime scene and determine the number of different weapons involved. They can compare the casing to those from other sources. They can also compare bullets to determine the possibility they came from the same weapon, and they can analyze weapons for characteristics which might match bullets and casing fired from it. Current examinations of firearms, bullets and casings use low-powered stereo binocular microscopes combined with high-energy illumination. The systems incorporate computers to assist in finding likely matches between a new casing or bullet and databases of ones previously collected, selecting potential matching items. Although somewhat automated, current techniques are still labor intensive, acting only to select likely matching items for manual review by a ballistics expert. The FBI and the ATF have each established a network of computerized systems to support the identification of guns, bullets, and casings; allowing member labs to share databases.

[0031] The Drug Fire program started by the FBI in the 1990's has established a network of computers in more than 40 forensic labs that exchange breech face striation information. Each member agency is responsible for classifying all its cases, and placing the information in computer. Any member agency can then compare evidence from its case to all other cases in the system. A second system, Bulletproof developed for the ATF, records striations on the bullet while the casings are categorized by a system called Brass Catcher. The national scope of these two programs is intended to assist in investigations of drug-related gangs with national networks.

[0032] Baldur (U.S. Pat. No. 5,390,108) presents a computer-automated bullet analysis apparatus. A microscope obtains and amplifies optical signals representative of the characteristics of the surfaces, and the optical signals are converted first to electrical signals and then to coded digital representations. The coded representations are stored in memory and are matched against one another to see if there is a match between the bullets. The ATF system is based upon that apparatus.

[0033] Land marks of 45 calibre bullets are normally photographed at 10× magnification and then enlarged to 4×, with at total enlarged ratio of 40×. 22 calibre long rifle bullets are commonly photographed at 20×, resulting in a total enlarged ratio of 80×. The reproducibility of land marks is better than for groove marks, especially for jacketed bullets. The width of groove marks is very wide compared to land marks in some cases; such as with 45 calibre bullets fired from an M1911A1 semi-automatic pistol. Imaging multiple groove marks at one time is difficult due to the need to focus at different depths.

[0034] Examiners compare the contour of the bullet surfaces using a comparison microscope. Not all of the bore surface characteristics will be reproducibly transferred even on consecutively fired bullets. In addition, there are always extraneous markings, which are not due to the gun bore surface, which an examiner must ignore.

[0035] Achieving proper illumination for detailed imaging is difficult with current matching systems. The metallic nature of the items causes glare and reflection to interfere with good imaging. Use of glancing light to highlight the relief structure interferes with distinguishing lands and grooves. Shadows create or mask features, and the depth of striations and indents cannot be determined. The automated analysis engines are computationally intensive and may be confused by manufacturing marks, shadow, glint, and focus. They may not distinguish between individual characteristics peculiar to the weapon, and manufacturing marks or incidental marks of no significance. The imagery and therefore the analysis is prone to variations due to differences in initial alignment, and to inconsistent lighting strength and direction from day to day and from lab to lab and technician to technician.

[0036] Current matching systems do not have the desired accuracy, speed, cost effectiveness, and ease of use. Due to the 3-D nature of the ballistic items, achieving proper illumination for detailed imaging is very difficult. The metallic nature of most of the items causes glare and reflection to interfere with good imaging. Use of glancing light to highlight the relief structure interferes with determining which marks are lands and which are groves. Shadows create or mask features, and the depth of striations cannot be determined. Details of the firing pin indentation cannot be seen without causing significant glare and shadow.

[0037] Current systems are not optimized for networking among many different users each having their own imaging system and sharing databases. Image orientation, focus, histogram, and size are not standardized. Current apparatus allows for variations in settings of focus, brightness, orientation, and size of the image according to the judgment of the user. The automated analysis engine is computationally intensive. It is confused by manufacturing marks, shadow, glint, and focus. It cannot distinguish between individual characteristics peculiar to the weapon, and manufacturing marks or incidental marks of no significance.

[0038] The imagery and therefore the analysis is prone to confusion due to inconsistent and aging lighting strength and direction from day to day and from lab to lab. Since there are no registration indices on the fired bullets or casings themselves, the matcher must try a range of rotations and translations for each potential match. Adopted rules, such as aligning the firing pin blow out to 3:00 (three o'clock) are of some assistance in manual placing of casings into the microscope holder. However, that feature is not always present in casings, and when it is, that procedure still allows for variations in rotational position of 5o or more. Manually aligning striations to the 9:00-3:00 horizontal is also prone to individual rotational variations on the order of 5o.

[0039] The current DrugFire system does not automatically extract and match features by their degree of significance, although it provides some manually assisted techniques for highlighting regions of interest. The current systems are designed to be a filter against the database, locating likely matching items in the database and presenting pages of 25 images at a time on a large screen monitor for a ballistics examiner to review and interactively compare. His comparison involves manually aligning two images on a split screen and looking for matching lines. Such matches may not be obvious without extensive manipulation of contrast, brightness, rotation, and translation of the two images.

[0040] A significant limitation to the automatic determination of matching images in a large database is the problem of distinguishing lands and grooves due to variations in the strength and directionality of the illumination. Striations may also run together, confusing the count. Other illumination-induced artifacts may also be created, particularly in the primer area about the firing pin indentation. Imprecise measurement of firing pin position and lack of detail on the shape of the indent, end points and width of striations, and other specific feature characteristics also result from illumination variations. As a result, visual images do not currently provide the capability for large database partitioning and searches based upon extraction and characterization of features.

[0041] The need is for a ballistics matching technology which is faster and cheaper than current techniques, which finds more correct matches with less manual intervention by a ballistics examiner, and which can exploit the current databases and enhance the performance of existing ballistics identification systems. The goal is to increase the capacity of the law enforcement community to identify increasing numbers of ballistic items, faster and with greater accuracy, and at minimum cost both in terms of manpower and system expenses.

[0042] The situation is analogous to that of fingerprint matching. As increasingly large databases are created, techniques are needed to partition those databases and to perform matches based upon feature characteristics, with full image comparison being performed on only a small percentage of the database considered candidate matches. Due to the nature of ballistic items and the distortions to which they are subjected, and to variations in illumination resulting from aging, positioning, focus, personnel, and laboratory differences, visual imaging does not provide sufficient consistency and reproducibility of feature location and characteristics to facilitate such precise matching.

[0043] Gun—device with barrel which fires a projectile, including pistols, revolvers, semiautomatics, rifles, and shotguns.

[0044] Bore—diameter and inside surface of a gun; it may be smooth or grooved

[0045] Riflings—spiraled, grooved markings inside a barrel

[0046] Trigger—mechanism used to fire the gun by releasing the hammer which strikes a firing pin housed inside the breech block

[0047] Firing Pin—mechanism driven into the primer area of a cartridge to initiate firing the projectile,

[0048] Primer—firing pin strike can be center fire or rim fire

[0049] Cartridge—case containing the projectile or bullet; it may be reloaded for repeated use

[0050] Forensic Item—any item used as a weapon, or item associated with a crime which may display marks related to the crime, including marks made on a human body

[0051] Ballistic Item—gun, bullet, shell casing, or other weapon, projectile, or element including the hands which may cause or receive marks or residue associated with firing a weapon

[0052] Infrared camera—an imaging device whose detectors are sensitive in a spectral band between 1 and 14 micron; the infrared camera may have an associated spectral filter which blocks or transmits segments of its band.

[0053] Active infrared imaging—heating or cooling the subject of the infrared image, including by sunlight, hot or cold air, immersion in fluids, application of flame or ice, or other means.

[0054] Image sequence—one or more images of a forensic item in which the camera is focused on specific features of the item

[0055] Reduced image sequence—an image sequence formed by selection of images which are of keenest interest to a ballistics examiner

[0056] Features—extended marks on a forensic item visible in visual or infrared imagery caused during the manufacturing process or during use. They include pits, scratches, embossing, gouges, residue, and machining flaws

[0057] Extracted feature sequence—a processed image sequence or reduced image sequence in which only features are shown

[0058] Image sequence focus montage—also referred to as a montage—combined sharp focus portions of multiple images in a sequence to make one or more composite images

[0059] Class characteristics—features related to a particular type of weapon or ammunition and include: calibre of weapon, type of ammunition, type of casing, number of lands and grooves and twist angle.

[0060] Tool Marks—residual markings left on an item which has been manufactured or worked using a tool. In the case of a ballistic item, it can be left by the manufacturing process, by incidental use, or by use as a weapon.

[0061] Weapon characteristics—features related to a particular weapon and may include firing pin impression, breech face marks, ejector gouge, extractor mark, striations, land and groove locations

[0062] Residue—materials deposited on a ballistic item, including blood, oil, gun powder, dirt, grease, fingerprints, body tissue, and building materials.

[0063] Manufacturers Mark—embossed or indented markings made during the manufacturing process, on cartridges this would commonly include type and calibre of ammunition such as “30-30 WIN”

[0064] Orientation—position of the ballistic item relative to the axes of the camera

[0065] Siblings—two bullets, bullet fragments, or shell casings known to have been shot from the same weapon with the same barrel.

[0066] Infrared imaging of guns, fired bullets and spent casings can provide detailed definition of characteristic features free from the shadowing, glint, and focus blur associated with visible light imaging. Although IR imaging is normally associated with measurements of temperature, the imagery from an IR camera results from emissivity and geometry variations in addition to thermal changes. The tool marks which are of forensic interest on bullets and casings are associated with significant emissivity differences. In particular, deep grooves such as firing pin indentations and primer edges create highly detailed observable features in IR imagery even at ambient temperature. Use of IR imaging for ballistics identification is therefore not intended to measure temperature differences, but rather to display and analyze emissivity and geometric differences associated with indentations and embossed features of the ballistic item.

[0067] The features seen in the infrared images do not vary in position or extent as a function of illumination as do visible images. Therefore they provide stable references for alignment with other images for comparison purposes. Additional details can be obtained by active IR imaging, in which the temperature of the gun, projectile or casing is varied. This provides a sequence of images in which certain features of interest are particularly apparent at specific temperatures. This process is suggested only when it is necessary to enhance very faint features.

[0068] Summary of Benefits of IR Ballistics Identification

[0069] The class characteristics of the ammunition and weapon include: calibre of ammunition, type of weapon, number of land marks, direction of twist of land marks, land mark width, angle of twist of land mark. All of this information can be obtained from infrared images, given that sufficient images at the correct temperature ranges are available.

[0070] The individual characteristics of the ammunition and weapon include the particular surface condition and shape of the bore, the particular striations imposed on the bullet, and the particular markings imposed on the casing. These characteristics can also be determined using infrared images. Even when caseless Teflon bullets are used, active infrared imaging may exploit minute markings transferred to the bullet by the barrel and firing charge. A rotating IR probe, similar to endoscopic cameras in medical use, can produce a detailed image of a gun barrel, which can then be matched against casings and bullets which are suspected of having been fired from that gun. In some instances, this may be preferable to making test firings from the weapon; particularly if the weapon is considered unsafe, or if it is necessary to preserve the weapon in its present condition as to residue etc.

[0071] The weapon itself should display identifying information such as the manufacturer's name and logo and serial number. If the serial number has been removed, use of infrared imaging can assist in recovering the information, since the emissivity of the area will be affected by attempts to file off or chemically etch off the serial number. By heating and cooling the weapon, a number of corresponding but different images can be obtained and all used to assist the reconstruction effort.

[0072] Characteristic weapons-identifying markings to be imaged and compared, include:

• • [0073] Scratches made on the bullet by the lands and grooves
  • [0074] Scratches made on the shell casing by the extractor and ejector of semiautomatic weapons
  • [0075] Indentation on the casing made by firing pin and breech face.
  • [0076] Indications of refilling and reusing the casing
  • [0077] Lands and grooves within the gun barrel
  • [0078] Trace items in residue deposited on the shooter's hand, within the gun, on the victim, on the bullet and casing, and on other targets.

[0079] Heat conduction analyses can be performed by heating the ballistic item and imaging it while it cools. Estimates of the depth and volume of indentations, striations, and gouges can be made based on their cooling rates. The material composition of each area of the item must be considered.

[0080] Current systems, such as DrugFire, compare an unknown ballistic item's image to all corresponding images in a database, producing a correlation value for each. Database images are then re-ordered based upon that correlation value, with the highest correlation ranked first. In controlled testing where the identities of all siblings are known, a measure of the accuracy and efficiency of the matching engine is the position of siblings in the re-ordering. The results shown below in the left column are taken from the DrugFire system manufactured by Mnemonics Systems Inc. The right column shows the use of a different matching engine (FlashCorrelation® patented by the inventor) with the same visual image database as used by Mnemonics. 1157 shell casings from 229 weapons were used for the tests. The images were all taken with a conventional videomicroscope camera. MIKOS did not have the opportunity to collect its own images of the casings. Therefore, no infrared images were obtained or used for this comparison test. The purpose of this table is merely to show how ballistic matching systems are evaluated. In a smaller test, the use of infrared imagery produced significant additional improvement in position of siblings over the use of visual imagery, with nearly all siblings clustered at the very top of the ranking.

[0081] “P” is a ranking order from 2% to 100%. Each image in the database is compared against every other, and the database is reordered by the degree of similarity with the target image. Each sibling of the target image (images of other casings fired from the same weapon) is located on the reordered list and included in the corresponding P value. Ideally all siblings would occur at the top of the rankings. The process is performed for each image in the test set database in order to obtain a statistical assessment of overall system performance.

[0082] Best indication of the relative performance of two systems would be to compare their results at P=2% since as P gets larger towards 100% any matching technique would produce similar results. In particular, at P=100% all matching techniques achieve 100% inclusion. Mnemonics did not report rankings for P less than 10%. If we extrapolate the Mnemonics results to 2%, the expected value was 25%. Comparing that with the 46% MIKOS value indicates that the MIKOS matching engine achieved 80% more detections at 2% than did Mnemonics.

[0083] The intent of the ballistics matching system is to find the best matches in the database and display them to a ballistics examiner who makes the final determination as to whether a match exists. The goal is to minimize the work of the examiner without sacrificing accuracy. The growing size of current databases requires a higher degree of automation to find links between crimes and suspects before either the statutes of limitations or the suspects expire.

[0084] The present invention relates to a method and apparatus for comparing patterns of marks found on ballistic items (including guns, bullets and shell casings) to determine whether they have common characteristics which would indicate that the bullet or casing has been fired from a particular weapon. The invention provides the ability to rapidly match images of an unknown ballistic item with a database of images of ballistic items including guns or ammunition fired from known weapons or unknown weapons, providing linkage between weapons or crimes or other events from which the guns, bullets or casings were recovered.

[0085] Infrared imaging of guns, fired bullets and spent casings can provide consistent and detailed definition of characteristic features free from the shadowing, glint, and focus blur associated with visible light imaging. Well-defined infrared imagery from casings and bullets is obtained even with the item at ambient temperature. The apparent temperature differences seen are due to variations in materials, and emissivity differences associated with geometry factors, and depth of markings. Therefore, the firing pin indentation, its surrounding area, the primer area, and the outer ring will all appear to be at different temperatures, although all are at room ambient. Use of the thermal imaging IR camera is therefore not intended to measure temperature differences, but rather to extract features based upon emissivity and materials differences. The resulting features can be automatically characterized, classified, and then matched against portions of the database having similarly characterized features. Since the features do not vary in position or extent due to imaging conditions, alignment of candidate matches is facilitated by

[0086] Active IR imaging, in which the temperature of the gun, projectile or casing is varied, provides a collection of images at the various temperatures. Certain features of interest are particularly apparent at specific temperatures. Features associated with different materials such as the primer, or with emissivity differences such as caused by abrasion, are more well defined when viewed with an IR camera. For a given type of gun or ammunition a set of temperatures can be determined such that the sequence of images resulting from heating or cooling the gun, projectile or casing to those temperatures provides an optimized data set for matching against a database. Matching can be done using standard image processing techniques such as optical or digital correlation, or using proprietary techniques such as Flash Correlation (U.S. Pat. No. 5,583,950 Method and Apparatus for N-dimensional Image Identification and Analysis.

[0087] If the ballistic item is heated and then imaged as it cools, the technique provides a sequence of images at various temperatures for each item. At certain temperatures, depending upon the composition material of the item, specific markings are enhanced. For example: serial numbers on a gun, manufacturers markings on a shell casing, striations on a bullet caused by the gun barrel, fingerprints, firing pin indentation and breech face marks on a shell casing can be characterized by size, shape, and relative location in a sequence of infrared images, as a function of imposed temperature. A feature template can be produced for each image in each sequence, by thresholding hot and cold values or other standard feature extraction techniques commonly used in image processing.

[0088] Any extended area of the infrared image with apparent temperature differences from the surrounding area may be considered a feature. Using the sequence of images or extracted feature templates, significant features can be extracted and characterized prior to use of the matching engine. Characteristics of the infrared features such as area, dimensions, depth, focus setting, variation in depth and apparent temperature, shape, inclusion of subfeatures, apparent temperature, location relative to center and edges of the ballistic item, ratio of perimeter to area, distance and vector to other features, persistence or exclusion over a range of imposed temperatures, persistence or exclusion under specific spectral filters may be computed and used to characterize the set of features seen in an image sequence or montage. If visual images are also being processed, then the visual characteristics of features seen in the infrared may also be used to characterize the features for a particular ballistic item.

[0089] By storing feature characteristics in a relational database, possible matches can be more quickly located. In general it is not necessary to find all matching ballistic items, such as all sibling casings. A single positive match provides links to others already in the database. As an example, for an unknown casing, determine the characteristics of: (1) distance from firing pin indentation to the center of the casing, (2) depth of indent, (3) angle of breech face marks relative to the line from firing pin indent to center, and (4) existence of ejector gouge. Then locate other items in the database which have some or all of the same characteristics. This is referred to as partitioning the database into candidate matches and other items. Candidate matches are then subjected to further processing. The corresponding image sequences or montages can be compared and those not sufficiently similar excluded from the candidates list. Remaining candidates are then presented for review by a ballistics examiner.

[0090] Selection of features to be characterized, and the characterization process, can be fully automated or manually assisted. Partitioning significantly reduces the search time required to look for matches, but requires knowledge about the variations which may occur in firings of a particular weapon. For example, changing the ammunition size or type used will change the markings imposed by the weapon. Therefore, in conducting a search against a database, to reduce the occurrence of false negative results, the criteria for including a database item as a candidate matching item must be considered relative to possible variations such as: whether the weapon has interchangeable barrels, whether it might be used with different sized ammunition, whether it might have been cleaned, whether it might have had heavy use between the database entry and the current characterization.

[0091] The precise extraction and matching of feature characteristics which is the method of this patent cannot be effectively performed on visual images due to the nature of the ballistic items, which produce illumination artifacts such as shadows and glint, and cause confusion of lands and grooves, and obliteration of fine details in deep markings such as firing pin indentations.

[0092] Class characteristics of ammunition and weapons include: calibre of ammunition, type of weapon, number of lands, direction of twist of land marks, land mark width, angle of twist of land mark. All of this information can be obtained from infrared images.

[0093] Individual characteristics of the ammunition and weapon include: the particular surface condition and shape of the bore, the particular striations imposed on the bullet, and the particular markings imposed on the casing. These characteristics can also be determined using infrared images. Even when caseless Teflon bullets are used, active infrared imaging may exploit minute markings transferred to the bullet by the barrel and firing charge. A rotating IR probe, similar to endoscopic cameras in medical use, can produce a detailed image of a gun barrel, which can then be matched against casings and bullets which are suspected of having been fired from that gun. In some instances, this may be preferable to making test firings from the weapon; particularly if the weapon is considered unsafe, or if it is necessary to preserve the weapon in its present condition as to residue etc.

[0094] The weapon itself should display identifying information such as the manufacturer's name and logo and serial number. If the serial number has been removed, use of infrared imaging can assist in recovering the information, since the emissivity of the area will be affected by attempts to file off or chemically etch off the serial number. By heating and cooling the weapon, a number of corresponding but different images can be obtained and all used to assist the reconstruction effort.

[0095] In matching casing faces, the database can be characterized according to:

• • [0096] Distance off center of firing pin indent.
  • [0097] Depth of firing pin indent.
  • [0098] Percent of face area having breech marks.
  • [0099] Depth of breech marks.
  • [0100] Angle between breech marks and firing pin vector, which connects the deepest indentation point with the closest spot on the casing edge.
  • [0101] Position of ejector marks relative to firing pin and breech face marks.

[0102] Images in the database can be oriented such that the flare-out of the primer is pointing to 3:00 (three o'clock) if it is not symmetrical; if it is symmetrical, then the firing pin indentation vector is set to be pointing to 3:00 if it is off-center; if it is also centered, then the breech marks are set parallel to the horizontal (3:00-9:00).

[0103] For bullets, the database can be characterized according to:

• • [0104] Calibre of bullet
  • [0105] Material
  • [0106] Length
  • [0107] Number of twists
  • [0108] Length of striations of maximum depth
  • [0109] Number of striations vs. Length
  • [0110] Relative positions of end points of striations.

[0111] For casing sides the database can be characterized according to:

• • [0112] Calibre of bullet
  • [0113] Material
  • [0114] Presence of ejector mark.
  • [0115] Presence of extractor mark.
  • [0116] Number of striations vs. Length

[0117] Images in the casing sides and bullet databases should be formed as composites of the multiple frames taken as the bullet or casing is rotated. The composite images can be oriented so as to align striations with the horizontal plane of the image. Due to spiraling of the lands and grooves, image segments must be composed to create an image of the resulting striation pattern from the various segments imaged.

[0118] For images derived from thermal probes of gun barrels, the database can be characterized according to:

• • [0119] Calibre weapon
  • [0120] Twisted bore or not.
  • [0121] Number of lands and grooves
  • [0122] Angle of twist.
  • [0123] Relative positions of start and stop points of lands and grooves.

[0124] The resulting strip image should be formed into a 2-dimensional image as if the gun barrel were sliced open and laid flat, and should be oriented such that the lands and grooves are horizontal in the image.

[0125] Since existing databases of ballistic images are all taken in the visible spectrum, utilizing those databases requires that new images also be taken in the visible domain. Due to the superior advantages of infrared imaging, it is anticipated that at some time in the future IR ballistic imaging will become standard. Meanwhile, IR images can begin to be collected for current and future use, and also to aid in exploitation of the existing databases.

[0126] By imaging in both IR and visible bands, extracting and characterizing features in each band, and comparing the results, apparent visible features which are in fact illumination-induced artifacts can be eliminated from the characterization of a ballistic item prior to matching against the database. Any true visual feature will also appear in the IR image. Eliminating artifacts will reduce the false positive error rate in visual matching.

[0127] True visible features such as striations may suffer from apparent reversal of deep and tall (e.g. land and groove) markings due to the angle of illumination. The comparable IR feature can be used as a reference to locally vary the gray-scale allocation (look-up table or LUT) in the visible image to best match that of the IR image. The result will standardize the appearance of the striations in the visible image, and improve the accuracy of the matching system.

[0128] Certain markings imposed by a manufacturer, such as the calibre and manufacturer's identity on shell casings, have a characteristic depth or height which facilitates separation of those markings based upon their apparent temperature difference in infrared images. The distinction between those features and others may be further enhanced by heating or cooling the ballistic item. A template may be made from the infrared sequence which can be used to separate the manufacturers and weapons marks in the corresponding visible images. This processing step allows for separate consideration of the two sources of marks, with the realization that the two types of marks may overlap and so subtracting one type may create changes in the feature characteristics of the other which must be accommodated in the matching engine.

[0129] Infrared imaging can employ optical filters to assist in determining the presence and composition of gunshot residue, as well as blood, body tissue, building materials and other matter deposited on bullets during their trajectory. Nitrocellulose forms carbon and the oxides of nitrate and nitrite. Other components may contain barium, antimony, cooper, and lead oxides or salts. Center core primers, found in most ammunition, traditionally have contained all four chemicals, but lead is now less prevalent, and rim fire primers, used almost exclusively for .22 calibre, often have no barium or antimony.

[0130] By the use of filters, the presence of residue on the ballistic item can be determined and classified. Apparent features of the ballistic item which are actually residue can be ignored for purposes of automatic matching against a database. This is particularly useful in the case where residue produces an apparent feature or obliterates existing features. If residue is detected, the system can provide instructions to the system user that the particular ballistic item needs to be cleaned prior to further imaging.

[0131] Infrared imaging of the hands of suspects can also utilize spectral filters to search for gunshot residue. This provides a possible immediate testing capability when a firearms investigator is not available, or the scene is too contaminated to facilitate clean lifting of debris from the suspect for later analysis. By combining infrared imaging of the hands and face of the suspect, the issue of chain of custody of the hands samples is eliminated, since infrared images of each person's face is unique. If the infrared camera annotates date and time, it minimizes the level of training and time required at the crime scene. Lift samples can be taken and studied via chemical analysis using a scanning electron microscope, as is traditionally done, in addition to the infrared analysis. For this application, an IR camera with automatic sequencing of optical filters and video or digital output recording provides the best setup for archival purposes and to support future analysis.

[0132] For the future, increasingly sensitive imaging and matching techniques are required: Teflon-coated bullets do not pick up land and groove impressions well. Caseless bullets have been developed which leave no shell casings after firing. The weapon used is an electronic .223 calibre rifle, called Lightening Fire, made by Jaguar Sport. The shell exists but is constructed of propellant only. When the trigger is pulled, an electric charge, not a firing pin, detonates the propellant, burning the entire casing. The combination of the self-destroying shell case and Teflon bullet will provide very little evidence for evaluation. Active infrared imaging of such bullets may provide sufficient information for identification and matching.

[0133] A composite image or images can be created by combining the best focused local image of each true feature of a ballistic item to create an image of the entire item in which each feature is in its relative position and in focus. The montaged images can be displayed to the ballistics examiner and/or first used in automated correlation processing to determine candidate matching items. This step can be performed for either visible or infrared image sequences and matching procedures.

[0134] The apparatus consists of the following components:

[0135] 1. Infrared imaging microscope having radiometric calibration for each image frame output, such that a given gray level corresponds to a particular apparent temperature. Variable focus optics allow for detailed in-focus imaging over the full range of depth and height of the ballistic item features.

[0136] 2. Shroud to avoid ambient light striking the ballistic item to cause reflections or heating.

[0137] 3. Holders for shell casings such that the back end is viewed normal to the camera axis.

[0138] 4. Holders for shell casings such that the side is normal to the camera axis and the casing can be rotated for a full 360o image.

[0139] 5. Holder for essentially undeformed bullets such that the bullet can be rotated and all of the surface can be imaged normal to the camera axis.

[0140] 6. Holders for deformed bullets such that multiple images can be taken which will encompass the entire surface area. Assume the bullet may have no obvious axis or center; the need is to completely image the surface. Multiple positionings may be needed.

[0141] 7. Holder for gun which facilitates operation of an infrared probe which has a helical scanning rotating head and forms an infrared image of the inside of the barrel of a gun as it cools.

[0142] 8. (Optional) Heater subsystem which can be on-line: radiant heat lamps, hot air, direct contact electric heat; or off-line: boiling in water or other liquid, heating in a controlled oven.

[0143] 9. (Optional) Spectral filters, which can be used to obtain additional image information such as the composition of the ballistic item, including material of the casing, material of the bullet, type of primer. Alternately, the system user can determine these characteristics.

[0144] 10. Feature Extraction Engine, which can be image processing software, firmware or hardware to locate local areas of interest in the image.

[0145] 11. Feature Characterizing Engine, which can be image processing software, firmware, or hardware to perform measurements of the features and associate those measurements with the image in a database.

[0146] 12. Focus position indicator, which annotates each image in a sequence with the focus position at which it was imaged.

[0147] 13. Image montage generator, which determines the best-focused image of each feature, and generates a composite image or images in which all features are present and each is in focus.

[0148] 14. Matching engine which correlates a montaged image of an unknown ballistic item against images in a database and rank orders or thresholds the results to produce a list of candidate matching items.

[0149] 15. Examiner workstation 100 which interacts with the ballistics examiner and displays the candidate matching item images, feature maps, correlation values, and characteristics of the ballistic items and their comparisons. The workstation 100 allows him to input queries and receive responses in display or hard copy format. It generates, maintains, and accesses databases of ballistic item images and features and information annotated by the user. It also includes a highlighter function which allows examiner to designate features of interest in an unknown ballistic item, for matching against a database. The highlighter can utilize a light pen, touch screen display, graphics tablet, or other interactive device.

[0150] 16. For Visible image matching, the apparatus also includes a video microscope with matching lenses to the IR microscope, and a database of visible images.

[0151] 17. Image processor subsystem acquires images from the cameras including either direct digital output or digitized analog output of the infrared and visible cameras. It standardizes image orientation including rotation, translation, and alignment based upon features in the image.

[0170] A ballistic item 10 is placed in a holder 12 and surrounded by a shroud 14 covering it and an infrared camera 16 such that external lighting and heating sources are blocked. The camera focus mechanism 18 is varied over a range such that all details of the infrared image of the ballistic item are clearly captured in a sequence of infrared images 20.

[0171] Optionally, one or more spectral filters 30 can be installed and additional sequences of infrared images obtained. Optionally, a heater 32 can be used to raise the temperature of the ballistic item and additional sequences of infrared images obtained for the item at the elevated temperature and as it cools.

[0172] A controlled light source 110 is then turned on to illuminate the ballistic item and a video camera 116 is used to produce a sequence of visible images 120 by varying the focus mechanism 118.

[0173] Each image is annotated with date and time, workstation #, item temperature, focus setting, and item reference number. The focus and image capture processes can be automated such that a succession of minute variations in focus is performed and an image taken at each step, or the focus and image capture can be manually controlled using an examiners workstation 100 consisting of a display screen 22 and input controls 24 including any combination of keyboard, mouse, voice, or similar device. The workstation 100 also contains highlighting device 90 for manually specifying areas of images or textual information of particular interest to the examiner. The highlighter can be any combination of touch screen, lightpen, graphics tablet, or similar device. The display has the ability to mosaic several infrared 20 and visible 120 images on a single screen.

[0174] Text information is entered which identifies the ballistics item and related information such as case #, weapon type, ammunition type, location where found, etc. That information can be read from an evidence tag using a bar code reader 28 or input through the controls of the examiners workstation 100 such as by keyboard. The text information can be displayed on the screen 22 along with the corresponding annotated image.

[0175] Both text information and image sequences are stored in an infrared image sequence database 26 and a visible image sequence database 126.

[0176] The sequences of visible images are processed to extract and characterize apparent features at 142 using any of various standard automated image processing techniques or by manual highlighting by the examiner. Characterization a minimum includes the relative positions of features, their shape, their area and perimeter length, and variation in gray scale distribution within the feature. Similar processing is performed at 42 on the infrared sequences using the same or similar processing.

[0177] For each visible feature, one image is selected from the sequence in which that feature is in sharp focus. The feature area of that image is extracted and used to create a montaged visible image 138 in which each feature is shown and each is in sharp focus. The same is done for the infrared sequence to create a montaged infrared image 38. Each montaged image is associated with the characterizations of the associated features at 42 and 142.

[0178] The characteristics of the montaged visible image 138 and montaged infrared image 38 are compared at 136. Any feature of the visible montaged image 138 which does not have a corresponding infrared montaged feature in image 38 is removed from image 138. Correspondence requires at a minimum overlapping locations and similar shapes. Those removed visible features are considered to be illumination-induced artifacts. Any visible feature which has a corresponding infrared feature, but which differs in gray scale distribution from the IR feature is subjected to variation in its gray scale allocation or LUT 134 to find the best correlation with the corresponding infrared feature. Those visible features are considered to have illumination-induced gray scale reversals. Any infrared feature which does not have a corresponding visible feature is considered to represent a possible true feature hidden in the visible image due to shadow. At the option of the examiner, such features can be (1) copied from the infrared montaged image to the visible montaged image, (2) annotated such as in color on the visible montaged image, (3) tested by the use of spectral filters and/or heating to determine if it results from residue, in which case the item should be cleaned and re-imaged.

[0179] The resulting montaged infrared and visible images, along with their characteristics and textual information are entered into a database of infrared characterizations 50 and enhanced visible characterizations 150 of unknown ballistic items. The enhanced visible characterization can then be used with current ballistic identification methods and apparatus, producing more accurate results due to the elimination of illumination-induced artifacts, and the detection of hidden features due to shadow.

[0180] When infrared imaging alone is used for ballistics identification, without use of corresponding visible images, then components 116, 118, 120, 126, 138, 142, 134, 150 and references to visible images, sequences, features, and montages can be eliminated from the apparatus description.

[0181] A ballistic item 10 is placed in a holder 12 and surrounded by a shroud 14 covering it and an infrared camera 16 such that external lighting and heating sources are blocked. The camera focus mechanism 18 is varied over a range such that all details of the infrared image of the ballistic item are clearly captured in a sequence of infrared images 20.

[0182] Optionally, one or more spectral filters 30 can be installed and additional sequences of infrared images obtained. Optionally, a heater 32 can be used to raise the temperature of the ballistic item and additional sequences of infrared images obtained for the item at the elevated temperature and as it cools.

[0183] Each image is annotated with date and time, workstation #, item temperature, focus setting, and item reference number. The focus and image capture processes can be automated such that a succession of minute variations in focus is performed and an image taken at each step, or the focus and image capture can be manually controlled using an examiners workstation 100 consisting of a display screen 22 and input controls 24 including any combination of keyboard, mouse, voice, or similar device. The workstation 100 also contains highlighting device 90 for manually specifying areas of images or textual information of particular interest to the examiner. The highlighter can be any combination of touch screen, lightpen, graphics tablet, or similar device. The display 22 has the ability to mosaic several images on a single screen.

[0184] Text information is entered which identifies the ballistics item and related information such as case #, weapon type, ammunition type, location where found, etc. That information can be read from an evidence tag using a bar code reader 28 or input through the controls of the examiners workstation 100 such as by keyboard. The text information can be displayed on the screen 22 along with the corresponding annotated image.

[0185] Both text information and image sequences are stored in an image sequence database 26.

[0186] The sequences of infrared images are processed to extract and characterize apparent features at 42 using any of various standard automated image processing techniques or by manual highlighting by the examiner. Characterization at a minimum includes the relative positions of features, their shape, their area and perimeter length, and variation in gray scale distribution within the feature.

[0187] For each apparent infrared feature, one image is selected from the sequence in which that feature is in sharp focus. The feature area of that image is extracted and used to create a montaged infrared image 38 in which each feature is shown and each is in sharp focus. If there is the chance that debris may remain on the ballistic item, then apparent features may in fact be debris. This event can be tested for by comparing corresponding focus images using different spectral filters 30. Apparent features which persist through a range of filters are considered actual features. Each montaged image is then associated with the characterizations of the associated features at 42.

[0188] When the unknown ballistic item characterized in 50 has been identified or linked with other known items, by a ballistics examiner or an automated system, its file is move to relational database 60 which then includes (1) textual information related to the case, its disposition, location of the item, names and dates, weapon information and links to other forensic and law enforcement databases; (2) images which may include the montaged feature images alone or also the image sequences, and may also include highlights created by a ballistics examiner and corresponding notes, which should be displayed in color for emphasis; and (3) feature characteristics including a summary of the number and types of features seen, and details on each feature including type, shape, size, location, and variation in gray scale and edge effects.

[0189] Database 60 will contain characterization of known or linked ballistic items. When an unknown item 10 is presented for identification, it is processed as detailed above to produce its characterization at 50. The resulting characteristics are used to select initial candidates from the database 60 based upon text, image, and feature characteristics which are relatively immune to error or variation. For example, the calibre of ammunition. In matching shell casings, if the unknown firing pin indentation is centered, only database entries with centered firing pins are considered as potential candidates. The presence or breech face markings, ejector or extractor marks may also be considered relatively immune to error or variation.

[0190] The initial candidate matches are then further processed using the text matching engine 70 which might provide for example the date of manufacture of the weapon, meaning that all ballistic items collected prior to that date need not be considered as matches. Other information is compared and scored as to similarity, such as information about the type of crime associated with the ballistics item, the locale where the item was collected, the presence of other similar items at the same collection, etc. The similarity score will generally not exclude candidates from further consideration, but may influence their rank ordering in presentation to a ballistics examiner for consideration below.

[0191] Remaining candidate matches are then further processed using the feature matching engine 72 which first compares summary characteristics such as the number and type of features, and then compares the details of each feature of the unknown and candidate items. Various metrics or scoring techniques can be defined to calculate a goodness of match based upon the feature characteristics. Fingerprint matching and face matching technique are especially suitable, with Prokoski et al. U.S. Pat. No. 5,163,094 as an example. Candidates which do not correlate sufficiently with the unknown item are not longer considered.

[0192] Remaining candidate matches are then further processed by correlating the montaged images using an image processing technique such as Prokoski U.S. Pat. No. 6,173,068 to produce an image correlation value. Other image processing comparison techniques may be used. The remaining candidates are then rank ordered based upon their text similarity score, their feature characteristics goodness of match, and their image correlation value. Various algorithms for performing the rank ordering can be used. An effective one is to assign a rank ordering based on each of the three measures, and then perform a composite rank ordering based upon the ordinal sum of the component rank orderings.

[0193] For various reasons it may be desirable to use only one or two of the three comparison techniques.

[0194] The top placing candidates are presented to the ballistics examiner for review on the display 22. Using interactive controls 24 he can manipulate the imagery to perform further visual matching of simultaneously displayed unknown and candidate text, feature characteristics, and imagery. His decision 78 for each candidate is either that it is a match or is not a match for the unknown item, and the information in database 50 is transferred to database 60. When he determines that a match has occurred, then he indicates through the control mechanism 24 that the previously unknown item is now linked to a particular candidate 80, If he exhausts the top placing candidates, he then indicates that the unknown item has no match 82 in the existing database as of the current date.