The Crime Labs Role In Shooting Reconstruction

Not all of the reconstruction of a shooting incident is done at the scene. A substantial part is often done off scene at the crime laboratory. For example, trace evidence and gunshot residue are documented in the lab; firearms testing is also laboratory work.

It is not uncommon for fired bullets recovered at crime scenes and from shooting victims to have tiny bits of material adhering to their surfaces as a result of striking things. This material is generally described as trace evidence. Typical trace evidence recovered from fired bullets includes blood, hair, tissue, fibers, paint, wood, glass, and so forth. With hollow-point bullets, which have a cavity in the nose, it is particularly common for this type of evidence to be present. As such a bullet goes through various different layers before it finally stops, tiny fragments are built up within the cavity. The result is a veritable "archaeological history" of where the bullet has been. Soft lead bullets are also prone to collect material on their surfaces. Even though the firearms examiner may not have the expertise to analyze and identify this trace evidence, recognizing its importance and getting the proper person involved are important parts of the job.

Gunshot residue testing is conducted to determine the approximate distance of a shot. This testing requires the use of chemicals and other items that are part of a laboratory environment.

As described in chapter 3, when a firearm is discharged, a cone of debris exits the end of the barrel behind the bullet or shot pellets. This debris consists of soot and gunpowder particles. The soot, being lighter, travels only a foot or so at most. The gunpowder particles travel varying distances depending on their shape. Spherical or ball powder travels the farthest and disk or flake powder the least distance. Flattened ball powder falls in between. In general, gunpowder particles are expected to strike anything within arm's length of the end of the barrel.

The amount of soot produced as well as the amount and distribution of gunpowder particles vary by manufacturer and by load. For example, two different brands of cartridges of the same design fired from the same distance may produce different residue patterns, as shown in the photograph.

A blissfully ignorant person might assume that one shot was fired from a different distance than the other, when in fact they were both fired from the same distance using different brands of ammunition. Once again, this is why it is important to have a well-trained examiner involved in the examination and interpretation of the evidence.

Precision target shooters are aware that consistent results depend on consistent loads and are careful to ensure that everything they can

0 0

Post a comment