Firearms and Toolmarks in the FBI Laboratory, Part 2, by Schehl (Forensic Science Communications, April 2000)
April 2000 - Volume 2 - Number 2
Firearms and Toolmarks in the FBI Laboratory
Sally A. Schehl
Forensic Science Communications
Forensic Science Research Unit
Federal Bureau of Investigation
Firearms examiners also conduct analyses dealing with toolmark identification, which involves the identification of a toolmark as having been produced by a particular tool. Though a tool can be thought of as the harder of two objects used to mark the softer object, a toolmark examination refers specifically to the analysis of an object used to gain a mechanical advantage (a more common definition of tool) and the objects bearing toolmarks or impressions from such use.
|As with the identification of firearms, the examination of tools and evidence bearing the marks of tools is based upon observable class and individual characteristics. Pliers and screwdrivers, for instance, can be eliminated as having produced certain toolmarks if those impressions are significantly larger or smaller than the width of the tools’ grasping jaws or blades. Like the size and shape of a tool’s working surface, the distance between a toothed instrument’s teeth is considered a class characteristic. Individual characteristics, produced during manufacture and use, are unique to a particular tool or toolmark but can include noticeable defects such as missing or partial teeth, raised metal nodes or ridges, distinctive signs of wear or damage, or a broken tip or blade.|
|Associated tool, wires, and plates
in a toolmark case
|Spacing between teeth in gripping or
cutting instruments can play a major
role in forensic toolmark
The conclusions reached by examiners analyzing toolmarked evidence are the same as those reached in firearms examinations: identification, exclusion, and no conclusion. With regard to tools, an identification signifies a match between two toolmarks or a match between a tool and evidence bearing toolmarks; a nonidentification denotes a lack of association between two items of evidence—the possibility that a tool produced a given mark or that two marks were produced by the same tool is excluded. No conclusion, as in the examination of firearms-related evidence, indicates insufficient corresponding microscopic characteristics and the consequent inability of the examiner to classify the evidence as either an identification or an exclusion.
Additional information on the forensic examination and identification of tools and toolmarks is available in the Toolmarks Examinations section of the Handbook of Forensic Services.
Before examiners conduct any of the specialized microscopic examinations involved in the identification of firearms and toolmarks, evidence submitted to the FTU is subject to preliminary processing. Physical science technicians are responsible for the inventory of incoming evidence and must verify that all items described by a contributor as having been sent to the Laboratory have actually arrived. FTU technicians label each piece of evidence as either a Q or a K, with Qs referring to questioned items and Ks denoting known specimens. Bullets, cartridge cases, shotshell casings, and other ammunition components are given Qs; firearms and tools are given Ks. All submitted items are individually marked with the appropriate Laboratory Number and listed on a worksheet that is maintained with the evidence for the duration of the case examination.
Evidence that must be examined by other units in the Laboratory prior to being examined in the Firearms-Toolmarks Unit is separated and distributed by the technician to those units as needed. When evidence does not require examinations other than those conducted by the FTU, the technician may begin preparing the submitted items for analysis following general case inventory. This preparatory handling may entail weighing and photographing specimens, researching printed literature on specific firearms and ammunition, writing notes on individual Qs and Ks, and microscopically measuring the general rifling characteristics of bullets—caliber, number of lands and grooves, and their direction of twist (right or left). Measurements of the latter defining features are made for known, test-fired specimens as well as for questioned bullets and can be compared to specimens in the General Rifling Characteristics (GRC) File, a computer database used to generate lists of firearms that could have produced such markings on fired ammunition.
|Firearms and other evidence recovered from crime scenes and field investigations are shipped to the FBI Laboratory and inventoried by technicians in the Firearms-Toolmarks Unit. Submitted firearms are marked as known specimens, or Ks; cartridges and other ammunition components of unknown origin are marked with Qs.|
Known bullet and cartridge case specimens generated through water tank test firing are maintained in the Reference Fired Specimen File of the Firearms-Toolmarks Unit following case completion for future comparison purposes. During the course of FTU casework, technicians may also enter the serial numbers of questioned firearms into the FBI’s National Crime Information Center (NCIC) database, where they are checked against lists of serial numbers from weapons registered as being stolen.
|The Reference Firearms Collection (RFC) contains over 5,100 handguns and shoulder firearms and is an invaluable reference in the identification of evidence firearms and firearms components, which can be matched against cataloged, intact collection specimens. Firearms in the collection are referenced for the locations of serial numbers and other identifying characteristics that assist in the classification of submitted weapons. The RFC also provides a supply of working parts for test-firing purposes in those instances when a firearm submitted as evidence has inoperable or missing parts and cannot be test fired in its received condition. In addition, firearms shown in bank robbery surveillance films can be compared with models from the RFC and potentially identified.||
The Standard Ammunition File (SAF) is a collection of over 15,000 military and commercial ammunition specimens of foreign and domestic manufacture. These specimens include whole as well as disassembled cartridges for each ammunition type and serve as standards in the identification of intact evidence as well as miscellaneous disassociated shot wads, pellets, shot cups, bullets, cartridge cases, and shotshell cases. A computer database was recently created for the information in this file, allowing comprehensive searches to be conducted on submitted ammunition components based on physical features.
|Examples of the disassembled cartridge and shotshell specimens maintained in the Firearms-Toolmarks Unit’s Standard Ammunition File, which facilitate the identification of ammunition components submitted as evidence|
The DRUGFIRE database allows examiners across the country to compare and link evidence obtained in the course of serial shooting investigations, especially those involving gangs and drugs. After test firing a weapon submitted as case evidence, FTU personnel can digitally capture and store images of bullets and cartridge cases using the DRUGFIRE system. These images can be compared to thousands of other images of bullets and cartridge cases entered by category and classification into the database by DRUGFIRE operators throughout the country. Hits are made when a system user finds a match between a specimen he or she added into the database and a previously filed specimen. With DRUGFIRE imaging, crimes committed in one locale can be tied to crimes committed elsewhere, and laboratories in many areas can access valuable forensic data.
Per agreement between the FBI and the Bureau of Alcohol, Tobacco and Firearms, all DRUGFIRE systems used in state and federal law enforcement will gradually be replaced with the National Integrated Ballistics Information Network (NIBIN). The NIBIN system will perform the same functions as DRUGFIRE and is expected to be fully operational within the next two years.