Comparison Microscope

The Firearm/Toolmark Unit examines a wide variety of firearms, components of fired ammunition, serial number restorations, gunshot residue pattern /distance determination analysis, Integrated Ballistic Identification System (IBIS), and toolmark related evidence. Firearms are often used during the commission of a crime or with criminal intent where injury or death occurs. Evidence, particularly weapons involved in these types of events, is often submitted to the laboratory for function testing. This examination determines if intentional alterations or defects exist in the manufacture’s operational design of the specific firearm. Function testing of a firearm is also performed to obtain test-fired exemplars which are compared to fired bullets and cartridge cases that are often collected at the crime scene.

The comparison microscope is the primary instrument used by the Firearm/Toolmark Unit in the examination and comparison of fired bullets and cartridge cases. This special type of microscope allows the examiner to compare the evidence components of fired ammunition to the test shot exemplars simultaneously. Unique microscopic individual characteristics are imparted upon the components of ammunition during the firing process. These individual characteristics or marks are often referred to as striae and are unique to a specific firearm. This type of examination allows the examiner to identify the components of fired ammunition as having been fired in a specific firearm.

           Cartridge Case Identification

It is quite common to find firearms with obliterated or eradicated serial numbers. This practice of removing the number from a firearm is often the result of attempting to conceal ownership of a weapon that has been stolen. With the serial number removed, law enforcement officials cannot establish who the legal registered owner is. The Firearm/Toolmark Unit utilizes a chemical technique that is often successful in the restoration of a readable number.

When a firearm is discharged at close proximity to an object, it deposits what is known as gunshot residue (GSR). GSR is often visible on the clothing of a victim of a shooting incident. A distance determination examination establishes how far away the muzzle of a firearm was when it was fired at the victim. This examination consists of a series of microscopic and chemical tests, firing the suspect weapon at predetermined distances, and a final comparison between evidence and test to establish an approximate proximity of the firearm.

Integrated Ballistic Identification System

The Integrated Ballistic Identification System or (IBIS) is a computerized digital imaging system which captures digital photographs of fired bullets and cartridge cases. These images are stored in a database and are electronically compared to one another. An IBIS Technician conducts a visual comparison of "high confidence hits" or images that display similarities for possible identification purposes. This system can generate investigative information and connect firearms evidence from previously non-related shooting events.

Toolmarks are impressions or marks that are produced by a tool or instrument on a receptive surface. Tools are commonly used to break into a locked building or to open a safe door. Toolmark impressions are also microscopic in nature and are the result of the imperfections found on the cutting surface of a tool. These marks are the "signature" or identifying characteristics of a specific tool. A microscopic comparison of the toolmarks left at a crime scene and test impressions produced by the suspect tool allows the examiner to identify the tool used in the crime.