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Firearms And Toolmarks

This section examines firearms, fired cartridge cases, bullets and tools used in a crime. Most of the examinations performed in the section include: Firearm function tests, microscopic examination of bullets, cartridge cases or other tool marks, serial or vehicle identification number (VIN) restoration, and gun shot residue test as it relates to the muzzle to target distance. The section may respond to crime scenes when requested. The section processes firearm and tool mark evidence related to animal cruelty, hunting, burglaries, robberies, assaults, murder and others.

Firearm Function Tests

Function tests are conducted on every firearm submitted to the Crime Laboratory. The extent of the test may depend on the case circumstance. Firearms are examined for cycle of fire, safety function, trigger pull, drop/friction tests and more.

Fire Arms Image

Firearm for examination, slide pulled back on right showing breech face, firing pin, extractor and ejector.

Microscopic Examinations

When a bullet or cartridge case is fired from a gun, markings from inside the firearm are imparted onto their surface. These marks are unique to each firearm. Once could say this is the “fingerprint” of the firearm. Most of these unique marks are left in the firearm during the manufacturing process at the factory.

One of the comparison scopes in the section used for the microscopic examinations.

Comparison of two fired 7mm Weatherby Magnum cartridge cases. There are clear circular machining marks on the breech face in the firearm from the manufacturing process which were stamped onto the head of the cartridges when fired.

Two 9mm Luger caliber bullets microscopically compared. The bullet picks up these marks from the barrel when it is fired.

A scale is utilized to measure a land impression on a fired bullet. These examinations are requested when there is no known firearm. The bullet type, shape, diameter, weight, the number of land and groove impressions and widths are measured. All of this information can be helpful in identifying a gun manufacturer.

Serial Number/VIN Restorations

Acid etching chemicals are used on evidence such as firearms, ATVs and Motorcycles when serial numbers or vehicle identifications numbers are removed to conceal ownership.

Serial number restored on the frame of a revolver

VIN restored on a stolen ATV

Gun Shot Residue and Distance Determination Tests

These tests are performed when it is necessary to determine how far away the shooter was from the target. The tests are conducted using the firearm in question. When a gun is fired it expels burned and unburned powder particles from the muzzle. These particles will land on the target within a limited proximity. The distance is determined when the gun is tested and the pattern is reproduced. The evidence and test shots are examined visually and chemically processed. The distance is determined by both of these reults.

Shirt submitted for GSR and distance determination tests, powder visible

Shirt processed for burned powder using the Modified Griess Test

Shirt processed for vaporous lead using Sodium Rhodizonate

Tool marks

The firearm section examines tool marks left at a crime scene to a tool taken from a suspect. When a tool is used on an object it often leaves an identifying mark behind. The section receives most often screw drivers and pry bars to compare against marks on safes. Bolt cutters are submitted to compare with the marks left on a cut padlocks or chains. Many other tools are submitted as well.

Cut lock compared to a test cut from the suspect’s bolt cutters

A tool mark from a gun safe cast with Mikrosil® and compared to a cast of a test tool mark using the suspect’s pry bar.

NIBIN Submission

Test fired cartridge cases and evidence cartridge cases may be sent to the Bureau of Alcohol, Tobacco, Firearms and Explosives Laboratory for entry into the National Integrated Ballistic Information Network. This can link a firearm or a cartridge cases from multiple scenes to one firearm.

Firearms Image #1