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Firearms And Toolmarks

The Firearms-Toolmarks Section of the Maine State Crime Laboratory receives and examines evidence related to firearms, ammunition, tools and toolmark involved in the commision of a crime. Frequently received items include rifles, pistols, cartidges, bullets, crowbars, knives and doorknobs. This section performs the following types of examinations:

• Firearms Function/Test Fire
• Microscopic Comparisons
• Serial Number Restorations
• Distance Determinations
• NIBIN

Examiners in the Firearms-Toolmarks Section test firearms suspected of being used in the commission of a crime. Just as no two fingerprints are identical, no two firearms will produce identical microscopic characteristics. The microscopic helical grooves left in a gun barrel when it is cast by a machine is called rifiling. When the gun is fired the bullet expands and rubs along these grooves as it is propelled along the barrel. Thus, the negative impressions of the rifiling are left on the bullet and are unique to each firearm manufactured. By measuring and comparing these land and groove impressions, the examiners determine if the firearm in question was used in the commission of a crime. The theory of microscopic tool examination is also applied in a similar manner to other tools used in crimes such as bolt cutters and crow-bars.

Microscopic Comparisons:

Comparison Microscope Images:

Serial Number Restoration:

Acid etching chemicals are used on firearms or other evidence such as engines to reveal serial numbers that have been removed in attempts to conceal ownership.

Distance Determination:

These tests are perfromed when it is necessary to find out how far the muzzle of a firearm was to the target. When a gun is fired it expells burned and unburned powder particles from the muzzle. These particles will land on the target if it is within a certain proximity. The same firearm and ammunition must be used and it is test fired at varying distances from the target. The targets are then processed chemically to compare the patterns with the evidence and determine the distance the firearm was to the target. Similar tests are done with shotguns.

NIBIN

In an effort to reduce gun violence in the State of Maine, the Firearms and Toolmarks Section of the Maine State Police Crime Laboratory participates in the ATF's National Integrated Ballistic Information Network (NIBIN) Program.

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