Firearms/Toolmarks

  • Description
  • Frequently Asked Questions

The Firearms and Toolmarks Section is responsible for the comparison of firearms, casings, projectiles and other evidence that may be associated through toolmarks. Toolmarks result whenever two items come into contact with sufficient force, such that one or both of the items bear markings resulting from the other item.

The most important method utilized in the Firearms and Toolmarks Section is comparison microscopy, which allows two items to be viewed simultaneously. Evidence projectiles, casings, and other items bearing toolmarks are compared to known items in order to determine consistency or inconsistency, both in class characteristics and individual characteristics.

What is Forensic Firearm Identification?

Forensic Firearm Identification is a discipline of forensic science which has as its primary concern to determine if a bullet, cartridge case, or other ammunition component was fired by a particular firearm.

What is Forensic Toolmark Identification?

Forensic Toolmark Identification is a discipline of forensic science which has as its primary concern to determine if a toolmark was produced by a particular tool.

Why are Firearm Identification and Toolmark Identification usually performed within the same group of examiners?

The process of matching bullets and cartridge cases to the gun that fired them is the same process used in matching toolmarked items with tools. In both disciplines the examiner looks for impressed and striated toolmarks on items of evidence. From an identification standpoint a firearm is merely a specialized tool which imparts striated toolmarks on bullets and impressed toolmarks on cartridge cases.

What kind of training and education is required to work as a Firearm and Toolmark Examiner?

Minimal educational requirements include a four year college degree in a natural science or chemistry along with the specialized post-college training in Forensic Firearm and Toolmark Examination. The typical post-college training program is a two-year instructor-student arrangement provided by one of the larger crime laboratory systems. The Firearms Examiner Academy offered by the Federal Bureau of Alcohol, Tobacco, Firearms and Explosives (BATFE) is an accelerated program which couples an experienced bench examiner with a new hire who attends an intensive study program at the BATFE laboratory in Maryland.

Can a bullet or cartridge case be positively matched to a gun to the exclusion of all other guns of the same type?

Yes, that is the core of the work performed by an examiner. However, it is not always possible to match a bullet or cartridge case to the gun that actually fired it. Such factors as impact damage, barrel fouling, and corrosion can make it difficult or impossible to make the positive association.

How is it possible to match a bullet or cartridge case to a particular gun seeing that a gun manufacturer may produce thousands of identical firearms?

Manufacturing processes produce gun barrels and gun breechfaces which conform to a mechanical standard, however, on a microscopic level the surfaces in a gun barrel or on a gun breech possess randomness as a result of such factors as the crystalline structure of the metal, machining defects, and the like. This randomness is the source of unique impressed and striated toolmarks created by each different firearm.

In addition to matching bullets and cartridge cases to guns what other types of evidence are processed by an examiner?

Muzzle-to-target distance determinations, serial number restorations, shooting incident reconstructions, physical matchings.

Is it possible to determine the type of firearm used in a crime by examining bullets and cartridge cases alone?

Yes, discharged cartridge cases and fired bullets display "class characteristics". Examining a bullet will reveal such data as the caliber, the number of lands and grooves from the rifling, the approximate land to groove ratio, the direction of rifling twist. Cartridge cases display the caliber designation and may also display characteristics unique to a particular firearm class.

What items are necessary for a muzzle-to-target distance determination?

On clothing it is necessary to assure that any moisture/body fluids on the garment are air-dried as quickly as possible to prevent deterioration of any gunshot residue products. Minimizing significant variables is necessary to assure the most reliable results. This is accomplished by providing the firearm and ammunition used in the commission of the shooting event.

On human skin it is necessary to provide high quality, properly exposed photographs of the residue pattern from a variety of angles. In addition to numerous overall photos from a variety of angles, a set of photos with a scale from the "trajectory perspective" - photos taken along the path followed by the bullet - is required.

Should crime guns be unloaded prior to submitting them to the laboratory?

As a general rule, yes. However, in some cases unloading a gun may jeopardize DNA, trace, or other evidence. In those cases it is necessary for the gun to be hand-carried to the lab where it can be tended to upon receipt. Loaded guns can never be mailed or otherwise shipped by common carrier. Loaded guns cannot be put into storage at the lab without prior special approval.

Can a gun that has been submerged in a lake, river, or the ocean be successfully matched to fired ammunition components?

Yes, the lab was successful in matching bullets and cartridge cases to a pistol that was submerged for exactly one year in a Mat-Su valley lake. Special handling of the firearm insured success. Submerged guns must remain completely submerged during the recovery process to prevent oxidation. Once the gun is removed from the water at the laboratory it is immediately flushed of debris, cleaned, completely dried, and re-oiled. Damp firearms tend to rust rapidly, quickly negating the possibility of a positive association of the gun to bullets and cartridge cases.

Can a fired bullet be matched back to the specific cartridge case that it was originally loaded in?

In theory, one should be able to find toolmarks from the case mouth on the fired bullet. In practice, toolmarks left on the bullet by the cartridge case are effectively eliminated by the rifling in the gun barrel.

Can live cartridges be compared to discharged cartridge cases or fired bullets?

Yes, it is important for the lab to have access to ammunition like that used in a shooting incident. A positive identification may hinge on the use of the exact same ammunition. Often the only source of this ammunition is the suspect. When ammunition is available, it should be seized along with the suspect firearm.

Can you determine when a firearm was last fired?

No, there is no practical test available to put an exact date on a discharge. However, revolvers often display "fresh flares" on the face of the cylinder. This finding often establishes the number of shots fired during the last use of the gun. As cylinder flares age they dull and are frequently rubbed or otherwise degraded during handling.

Can you determine the caliber of a bullet by the hole it produces?

Sometimes. Certain materials will preserve the exact diameter and cross sectional profile of the bullet. Aluminum street sign material often reveals the caliber and rifling class of the firearm that fired the perforating bullet. Other materials, such as clothing, plastic, rubber, etc. are too elastic. Large bullets can produce deceptively small holes. Each case is considered individually.

Can a Firearm Examiner prove murder?

No. Murder is the intentional taking of a human life. Laboratory testing cannot determine the intent of the individual holding the firearm when it discharged. It is the responsibility of a trial jury to consider the testimony of all of the witnesses, including the Firearm Examiner, and to consider the arguments put forward by the prosecutor and defense attorney in order to reach a verdict of murder, manslaughter, criminally negligent homicide or acquittal.

Does the lab or its examiners work civil cases or criminal cases outside of Alaska?

No. The lab is limited to processing evidence collected in the course of criminal investigations submitted by local, state, and federal law enforcement agencies located within Alaska. The current firearm/toolmark staff do not moonlight in their specialty.

Where can I find additional information about Forensic Firearm and Toolmark Identification?

You can contact the lab staff by phone or email. Additional resources can be found by visiting http:\\www.afte.org and http:\\www.firearmsid.com.

What is NIBIN?

Read about ATF's NIBIN proagram

Visit the National Integrated Ballistic Information Network website

Significant Firearm/Toolmark cases in the popular media:

Court TV
Forensic Files

In Harm's Way
Signed, Sealed, Delivered

History Channel
Dead Reckoning

Invisible Clues

Evidence Technology Magazine

A Tale of Three Bullets