Ballistics Identification: From discharge to conviction how CSI’s see the secrets
Drew McIntosh
Florida Southern College
Abstract
With television shows exploiting law enforcement and science, criminals think that they are
capable of out thinking the police and crime scene investigators by attempting to leave no trace
evidence behind at a crime scene. Crimes that are committed with the use of guns are sometimes
hard to solve. The reason for this paper is to explain the process and what capability Crime Labs
have to link bullets and shell casing to guns and suspects. This paper will also go in depth on
bullet striation marks, how they are caused, and unique to each firearm. This paper will also look
at the process of comparing bullets using technology and databases that law enforcement have at
their disposal. This data is important information which can help investigators link criminals,
guns, and motives based on bullets found at crime scenes.
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From the time that a crime is committed every second counts while a suspect is on the
loose. For the men and women of law enforcement, the evidence that is left behind holds clues
and secrets that citizens don’t realize they leave. During the commission of a crime involving a
gun the bullet holds many clues that can point the police in the correct direction of finding their
suspect. This paper will show the physical clues that are left behind by the shooter and how
Crime Scene Investigators use science and technology to find the shooter.
When a shot rings out there is a very short yet length process inside the framework of a gun.
From the firing pin hits the bullet’s primer causing striations and groves to be imprinted at
microscopic levels that can link a firearm to a shooter. The purpose of this paper will be to show
how a gun can be linked to a bullet by the groves and striations, and how when a bullet is found
at a crime scene how will the Crime Scene Investigator process the bullet in the lab along with
the comparison microscope process to see two bullets at one.
Guns are very complex machines that are comprised of hundreds of parts. Picking up a
gun and not knowing how to properly use it may result in great bodily harm. However picking up
the gun may be all investigators need to link a suspect with a weapon. Every time we hold or
touch an item we leave behind a very unique pattern called fingerprints. Fingerprints are created
when oils and residues on your fingers are transferred from the peaks of friction ridges to a
relatively smooth surface (Young and Ortmeier). Each finger in a human fingerprint is unique.
With a gun having a variety of functions and movements in order to allow it to fire, there many
places that fingerprints can be left behind. Gripping a firearm exposes the fingers of the gripping
hand to the handle of the gun. Pulling the trigger reveals portions of the index finger and
touching the slide or other parts of the gun can expose even more fingerprints of a suspect.
Fingerprints can either be seen by the naked eye or with the assistance of fingerprint powder.
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Once a print has been processed with a powder or a chemical, it becomes a latent fingerprint
(Young and Ortmeier). Since fingerprints are unique to each human it allows investigators to run
the fingerprints lifted from a firearm through a database composed of thousands of fingerprints.
This database is called AFIS or Automatic Fingerprint Identification System. The database
TOUCH DNA
A way to identify DNA is through the Combined DNA Index System also known as CODIS.
CODIS was created by the Federal Bureau of Investigations seeking to help investigators with
identifying suspects by providing computer programs to conduct DNA matches (LOFTUS).
CODIS enables local, state, and federal law enforcement crime labs to exchange and compare
DNA profiles (LOFTUS). CODIS organizes profiles DNA samples into indexes. These indexes
include: Convicted Offender, Forensic Index, Population Index, Victim Index, Unidentified
Persons Index, and Unidentified Persons Reference Index (LOFTUS).
When a DNA samples is collected from a crime scene, the samples’ profile can be added
to CODIS allowing the system an opportunity to find matches. If a match is found the two
agencies will confirm the match and then share information about the potential suspect.
TOPIC #2
Outside of the databases for external forensic evidence the internal instruments of the gun are
very important when investigators are looking on how to identify the weapon.
COMPARISON MICROSCOPE AND SCIENCE
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The main piece of equipment that investigators use for examining ballistics is a forensic
comparison microscope. A forensic comparison microscope is comprised of two microscopes
that are connected by and optical bridge. The optical bridge allows the examiner to view one eye
piece and examine two microscope stages with a spilt screen. Comparison microscopes are built
with a variety of accessories to allow investigators to attach bullets, cartridge cases, firearm
parts, and shot rounds. The microscope will have a video imaging system attached so that the
investigation will be able to see how the comparison is made for court records. (ASHRAF).
Firearm comparison gets attacked due to the lack of science and identification criteria. In
1993 the Supreme court in Daubert v. Merrell DowPharmaceurical that the expert testimony
must be related to a verifiable science. In relation to firearms identification, the examination of
evidence is based of patterns and off of pattern recognition. There is no science behind testimony
except for training and experience. This dilemma with the courts has unleashed many studies
behind ballistics identification. In 2006, a federally funded study by Benjamin Bachrach was
started to prove that there was an exact science behind the examination. Bachrach found that
using a computer and 3D imaging to create an analytical score based of the striations. The
computer determines whether or not the bullets are a match (ASHRAF).
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