Forensic Ballistics
For law enforcement personnel, a callout to a crime scene may begin a long and complex series of interlocking investigations into the nature, cause, and persons responsible for the incident. Specialists known as crime scene investigators assist law enforcement officers and detectives to uncover the clues at the scene. Because the United States has more firearms, and more firearms violence, than any other country, these clues often involve evidence left behind by firearms. Firearms have been used for hundreds of years. The world’s oldest gun was found by archeologists in China. They believe it was dropped on a battlefield in Manchuria in 1288. By the 1600s, firearms were becoming essential equipment for the armies of European nations, and helped pave the way for conquerors who
spread out across the globe to the Americas, Africa, Asia, and Australia. By the 1900s, millions of firearms, and the ammunition for them, were being mass produced. During this time, the science of forensic ballistics was developed to keep pace with the expanding number of crimes committed using firearms. This science examines firearms, bullets, and bullet behavior after being fired from a gun, and provides a quantitative, or measurable, way to compare crime scene evidence from multiple cases. The foundation of this science is an understanding of the construction of ammunition
and the mechanics of firearms.
As till now, There are many definitions proposed by forensic ballisticians about Forensic Ballistics. In a simple language,
Forensic ballistics is the scientific study of firearms, bullets, and bullet behavior after being fired from a gun.
After Calvin Goddard employed comparison macroscope and understood its importance in determining whether the same firearm fired the questioned bullet or not by examining under it, Many law enforcement agency found his work very tremendous and start employing comparison macroscope for the same. This science examines firearms, bullets, and bullet behavior after being fired from a gun, and provides a quantitative, or measurable, way to compare crime scene evidence from multiple cases. The foundation of this science is an understanding of the construction of ammunition and the mechanics of firearms.
After a crime involving firearms is committed, the main goals of Forensic Ballisticians is try to find out answers of following questions:
- Whether the same firearm fired the questioned bullet recovered from crime scene?; and this is done by 'Comparison'.
- Whether the cartridge case recovered from crime scene was used in suspect's firearm?; this is also done by Comparison.
- What is the estimated range of fire?; by Gunshot Residue (GSR) analysis and wound examination of victim.
- Whether the case is of Suicide or Homicide or Culpable Homicide?; GSR analysis and wound examination.
- What are the class characteristics of Bullet(s), Cartridge(s) and Firearm(s)?; Make, Model, Proof Marks, Caliber of bullet etc.
- What are the individual characteristics of Bullet(s), Cartridge(s) and Firearm(s)?; Toolmarks (such as striations, impressions etc.)
Though, the main work of the firearms examiner is essentially tool marks comparisons of cartridge cases and projectiles to associate them with specific weapons. However, firearms examiners are more than just experts in firearms identification and examination of ammunition. They can help determine the distance and angle from which a weapon was fired or tell whether a weapon could be fired at all. They also rebuild weapons, recover serial numbers, and reconstruct bullets. Chemists in the laboratory also analyze gunshot residue.
One of the interesting case that involved forensic ballistic examination was The Beltway Snipers
The Beltway Snipers
During a three-week period in October 2002, ten people were killed and three others were wounded as two snipers terrorized the region in and around the Baltimore–Washington metropolitan area. The arrest of John Allen Muhammad, 41, and Lee Boyd Malvo, 7, ended the ordeal. The semiautomatic .223-caliber rifle seized from them was ultimately linked by ballistic tests to eight of the ten killings. The car that Muhammad and Malvo were driving had been specially configured with one hole in the trunk through which a rifle barrel could protrude, so that a sniper could shoot from inside a slightly ajar trunk. The major break in the case came when a friend of Muhammad’s called police suggesting that Muhammad and his friend Malvo were the likely snipers. Muhammad’s automobile records revealed numerous traffic stops in the Beltway area during the time of the shootings. Another break in the case came when Malvo called a priest to boast of a killing weeks before in Montgomery, Alabama. Investigators traced the claim to a recent liquor store holdup that left one person dead. Fortunately, the perpetrator of this crime left a latent fingerprint at the murder scene.
Authorities quickly tracked the print to Malvo, a Jamaican citizen, through his fingerprints on file with the Immigration and Naturalization Service. A description of Muhammad’s car was released to the media, leading to tips from alert citizens who noticed the car parked in a rest area with both occupants asleep. The motive for the shooting spree was believed to be a planned plot to extort $10 million from local and state governments. Muhammad was sentenced to death and Malvo is currently serving life imprisonment without parole.
Just as natural variations in skin ridge patterns and characteristics provide a key to human identification, minute random markings on surfaces can impart individuality to inanimate objects.
Structural variations and irregularities caused by scratches, nicks, breaks, and wear permit the
criminalist to relate a bullet to a gun; a scratch or abrasion mark to a single tool; or a tire track to
a particular automobile. Individualization, so vigorously pursued in all other areas of criminalistics, is frequently attainable in forensic firearms examination. The high frequency of shooting cases means that the science of firearms identification
must extend beyond mere comparison of bullets to include knowledge of the operation of all
types of weapons, restoration of obliterated serial numbers on weapons, detection and characterization of gunpowder residues on garments and around wounds, estimation of muzzle-to-target distances, and detection of powder residues on hands.
BULLET COMPARISONS
Technically saying, the metal which the bullet is made of is softer than the metal which the firearm is made of. Bullets collected for comparison to a specific firearm are examined first to see if they are from a caliber that could have been fired from the submitted firearm. They are then examined to determine if the pattern of rifling impressions found on the bullet match the pattern of rifling questioned firearm has. If these class characteristics agree, the next step is to try to make a positive match between the individual characteristics that may have transferred to the bullet from the barrel. Located within the rifling impressions on a bullet can be microscopic striations or scratches like those seen on the bullet below.
Imperfections in the surface of the interior of the barrel leave striations on the projectiles. Striations have the potential to be consistently reproduced in a unique pattern on every bullet that passes down the barrel of a firearm. The key word in the previous sentence is unique.
Firearm examiners will attempt to find this unique pattern by following the procedures outlined below.
Examination of Bullets:
A
submitted firearm will be fired several times using a
water tank like the one on the left to obtain standards from
the firearm. Lids on the tank are closed and locked and the muzzle of the
firearm is placed in the open tube at the end of the tank and fired.
Friction from passing through the water slows the bullets down and they end up
on the bottom of the tank about halfway down its length. The tank is
approximately 3 feet wide, 10 feet long and 3 feet high.
Fired
standards, like those to the right, are examined first to determine if in fact
the barrel is producing striated marks in a unique and consistent pattern. Once
a consistently reoccurring pattern to the marks is identified on standards, the
standards are compared to the evidence bullets to see if the same pattern of
marks exists on the evidence. To make these comparisons the firearm examiner
will use.
A Comparison Macroscope
Notice that this is called a macroscope
and not a microscope. Microscopes typically use
objectives that are 100x and above. Magnifications typically used in firearms
identification are 5X, 10X, 20X, 30X, and 40X. It is not unusual however
to see these lower powered scopes referred to a microscopes.
All
firearm sections will have a comparison macroscope. The comparison
macroscope consists of two macroscopes mounted side by side and connected by an
optical bridge. There are two stages on the lower part of the macroscope that
the bullets to be compared are mounted on. The bullets are attached
to the stages using some type of sticky substance. Images of the bullets
travel up through the objectives, bounce off several mirrors in the optical
bridge, and are combined in a round field of view seen by looking into the
stereoscopic eyepieces. The resulting image will show the bullets mounted
to the stages, side-by-side, with a thin dividing line down the middle.
The images below show rifling impressions on a 32 caliber bullet at
progressively increasing magnifications.
The
stages that the bullets are attached to allow the bullets being examined to be
rotated on their axis and moved up, down, to the left, and to the right.
The bullets are rotated around to see if any microscopic similarities are
present. Most positive identifications are made on striations that occur in
land impressions and the best marks are usually near the base of the bullets like those seen below.
One of the biggest problems in making an
identification is that few evidence bullets are submitted intact. Most
are badly distorted, wiped and/or fragmented. The fragment seen below may
not look like much but even small fragments and badly damaged bullets can still
retain sufficient marks for an identification to be made.
Until
the questioned bullet is examined microscopically by a trained firearm examiner
you just don't know if it has marks of comparative value. The comparison
image below shows the above bullet fragment (right) compared to a standard
(left) fired from the submitted firearm.
Results
·
When
comparisons are made between firearms and fired ammunition the results can read
as follows:
- o Exhibit 1 (bullet) was identified as having been fired from Exhibit 2 (revolver).
- o This conclusion is reached after all class characteristics agree and a sufficient correlation between individual characteristics is found.
- o Exhibit 1 (bullet) could neither be identified nor eliminated as having been fired from Exhibit 2 (revolver). All comparisons were inconclusive.
- o This conclusion is reached if class characteristics agree but there is an insufficient correlation between individual characteristics.
- o Exhibit 1 (bullet) was not fired from Exhibit 2 (revolver).
- o This conclusion is reached if class characteristics disagree.
We have now discussed how bullets can be identified as having been fired from a firearm but what about the cartridge cases. WAIT TILL NEXT POST...
