Forensic Ballistics

Forensic firearm ballistics is the science of examining the characteristics of firearms, cartridges, and/or bullets found at a crime scene. Ballistic Forensics Specialists are tasked with tying this evidence to crime suspects. Examiners can also look for fingerprints on the weapon and cartridges, and then viable prints can be processed through fingerprint databases for a potential match.

By examining unique striations, or markings, left behind on the bullet as it passes through the barrel and on the cartridge as it is hit by the firing pin, spent rounds can be linked back to a specific weapon. Known exemplars taken from a seized weapon can be directly compared to samples recovered from the scene using a comparison microscope. Striation images can also be uploaded to any existing national databases. Furthermore, these markings can be compared to other images to link one weapon to multiple crime scenes. Like all forensic specialties, forensic firearm examiners are subject to being called to testify in court as expert witnesses.

Did You Know?
Even when serial numbers have been destroyed, ballistics forensics experts raised and record the original numbers to locate the registered owner of the weapon.

History of Ballistics and Forensics Ballistics

English: Comparison microscope.
English: Comparison microscope. (Photo credit: Wikipedia)

The ability to compare ammunition is a direct result of the invention of rifling around the turn of the 16th century. By forcing the bullet to spin as it travels down the barrel of the weapon, the bullet’s accuracy increases. The rifling in the barrel leaves marks on the bullet that are indicative of that weapon. Prior to mass production of firearms, each barrel and bullet mold was hand made by gunsmiths making each unique.

The first documented case of success in forensic firearm examinations occurred in 1835. A member of the Bow Street Runners in London matched a recovered bullet from a murder victim to a specific mold in a suspect’s home. This confirmed that the suspect made the bullet. Further evidence that the bullet maker was the perpetrator was found in his home and the evidence led to a conviction.

As manufacturing and automation replaced hand tools, the ability to compare bullets became impossible due to the standardization of molds within a specific company. However, experts in the field postulated that there were microscopic differences on each barrel left during the manufacturing process. These differences were a result of wear on the machines. Because each newly-formed weapon caused a tiny amount of wear in the machinery, each barrel would be slightly different from every other produced on that equipment. Each bullet fired from a specific barrel would be printed with the same marks, allowing investigators to correctly identify the weapon that fired a specific bullet.

Interesting Fact
In 1915, Charles Stielow was sentenced to death for the murder of his neighbors. He appealed Governor Charles Whitman, the Governor of New York. Whitman was not convinced of the evidence against Sitelow. Ballistics examiners determined that Stielow’s firearm could not have fired the bullets recovered from the victims. His conviction was overturned and he narrowly avoided execution for a crime he did not commit.

The Father of Modern Forensics Ballistics

In 1925, Major Calvin H. Goddard wrote an article for the Army Ordnance titled “Forensic Ballistics.” In it, he described the use of the comparison microscope in firearms investigations. He is generally credited with the conception of the term “forensic ballistics.”

Goddard with Comparison Microscope
Goddard with Comparison Microscope (Photo credit: Wikipedia)

In April 1925, Major Goddard established the Bureau of Forensic Ballistics in New York City with C. E. Waite, Philip O. Gravelle, and John H. Fisher. The Bureau was created to provide firearms identification services throughout America. The Bureau of Forensic Ballistics was the United States’ first independent criminological laboratory. Headed by Goddard ballistics, fingerprinting, blood analysis, and trace evidence were brought under one roof.

When the Bureau began publishing the American Journal of Police Science, edited by Goddard, now a Colonel, J. Edgar Hoover strongly encouraged his Special Agents in Charge to subscribe to it; Hoover personally supplied articles on fingerprint issues and FBI responsibilities for the journal. The following year, his agency contributed three articles for the journal’s series entitled “Organized Protection Against Organized Crime.” Hoover also sent representatives to a symposium that Goddard sponsored on scientific crime detection and Goddard soon became an advisor to the FBI when it established a Forensics Laboratory.

Throughout his life, Goddard researched, authored, and spoke extensively on forensic ballistics and firearms identification. He became an internationally renowned pioneer in the field; though not really the pioneer of ballistics, he is generally considered the father of modern forensic ballistics because of his efforts to expand the science. One area in which his team expanded the science of ballistics was in the creation of the Comparison Microscope.

Development of the Comparison Microscope for Ballistic Forensics

Philip O. Gravelle developed the comparison microscope for the identification of fired bullets and cartridge cases with the support and guidance of Goddard. It was a giant leap in the science of firearms identification. The firearm from which a bullet or cartridge case has been fired is identified by a comparison of the unique striations left on a projectile or cartridge.

English: (Photo credit: Wikipedia)

Gravelle mistrusted his memory. He knew that inspecting a single bullet at any given time required keeping the image in mind while inspecting the comparison bullet. This would naturally hinder scientific precision. The solution was simple: Create a microscope that would allow him to examine both at the same time.

Sir Sydney Smith also appreciated the idea, emphasizing the importance of stereo-microscope in forensic science and firearms identification. He took the comparison microscope to Scotland and introduced it to the European scientists for firearms identification and other forensic uses.

The invention of the comparison microscope by Calvin Goddard and Phillip O. Gravelle in 1925 modernized the forensic examination of firearms. Simultaneous comparison of two different objects at the same time allowed close examinations of striations for matches and a definitive statement could be made to the courts.

Testing the Comparison Microscope

One of the first true tests of this new technology was in the aftermath of the Saint Valentine’s Day Massacre in 1929. During the Prohibition Era, competing gang members were fighting over bootlegging operations in the city of Chicago. Members of the Chicago Outfit and the Egan’s Rats led by Al Capone attempted to remove all competition from Chicago by eliminating the North Side Gang leader Bugs Moran. The massacre missed Moran, who was not present but killed seven members of the North Side Gang.

English: Detroit police inspecting equipment f...
English: Detroit police inspecting equipment found in a clandestine underground brewery. (Photo credit: Wikipedia)

The murderers attempted to cover up their crime by posing as police officers, even dressing in police uniforms. Witnesses saw two “officers” leaving the scene, which implicated the Chicago police department as the perpetrators of the massacre. High levels of police corruption during that period made it seem likely that the police department committed the killings.

The investigation stalled until December 1929 when Fred Burke, a member of the Egan’s Rats, shot and killed a police officer in St. Joseph, Michigan. Officers searching for Burke were led to a home in nearby Stevensville. While Burke was not there, inside officers found an arsenal of weapons including two Thompson submachine guns. The Chicago police department was contacted and the weapons were brought back to Chicago for testing.

Goddard was asked to compare the weapons to collected evidence found at the massacre using his new ballistic-forensics technique. After test firing the guns, Goddard proved that the weapons were those used to kill the members of the North Side Gang. This proved that the Chicago police department was not involved. The successful use of Goddard’s technique was another step in the solidification of his place as the father of forensic firearm examination.

Forensics Examination of Firearms

A firearm collected during an investigation can yield viable evidence if examined. During a forensic firearm examination, specific evidence can be recovered such as weapon serial numbers, ballistic striations, fingerprints on the weapon’s surface, and more. Even a firearm found away from the scene of a crime can aid investigators working active crimes.

For instance, if a firearm is found in a ditch along the road and turned in to authorities, a forensic ballistic examination may tie the weapon to crimes committed using the striations. A partial print on the weapon or any casings which remain could lead investigators to a suspect of a crime.

Recovering Fingerprints on Firearms

Fingerprint recovery from the surface of firearms is done with cyanoacrylate (superglue) fuming. Firearms are placed in a specially designed fume hood which evenly distributes fumes instead of removing them. Liquid superglue is placed in a container and heated until it is in a gaseous state. The circulating fumes adhere to the oils left behind by the fingerprint, causing the print to turn white. The resulting white print can be enhanced with fingerprint powder to increase the contrast against the weapon’s finish.

Although the fuming technique is common, the recovery of fingerprints from the surfaces of a firearm is often challenging because of textured grips and the usual conditions of recovered weapons; most recovered weapons have been in the elements for some time. If fingerprints are recovered, they can be processed through fingerprint databases such as the Integrated Automated Fingerprint Identification System (IAFIS).

Various parts of the recovered weapon can also be tested for touch DNA, but contamination and analysis anomalies are common when only small samples are available for testing. Two such anomalies are allelic drop-out and drop-in, which are missing and added data in the genotype examined.

Recovering Serial Numbers from Weapons

Serial numbers became commonplace after the United States passed the Gun Control Act of 1968. This law mandated that all guns manufactured or imported into the country have a serial number. Prior to 1968 firearms either did not have a serial number or the serial numbers were not unique; many were reused by a manufacturer on multiple firearms. Clearly, this posed serious problems for prosecutors of crime.

If a recovered weapon has had the serial numbers altered or destroyed, examiners can attempt to recover the original numbers. The two main methods for the restoration of serial numbers are magnetic particle inspection and chemical restoration. It is recommended that magnetic particle inspection be performed first because of the nondestructive nature of the method. If magnetic particle inspection fails, chemical restoration is the next step in the forensic analysis.

If the serial number is successfully restored it can be used to help investigators track the weapon’s history, as well as potentially determine who owns the weapon. Firearm databases such as the National Crime Information Center of the United States and INTERPOL’s Firearm Reference Table can be used by investigators to track weapons that have been lost, stolen, or used previously in other crimes.

Recovering Weapon Serial Numbers Using Magnetic Particle Inspection

Developed as a method to detect flaws or irregularities in magnetic materials, magnetic particle inspection can be used on firearms to visualize the serial number underneath an area filed off. When performing this technique, examiners place the weapon in a magnetic field. The irregularities in the metal, in this case, the serial number, cause the field to deform.

Next, a solution of ferrous particles is added to the weapon’s magnetized surface. The particles will be attracted to the area where the magnetic field has deformed. Adding fluorescent particles to the ferrous solution can allow forensics examiners to use ultraviolet light to see the serial number.

Even a partial serial number may lead investigators to the owner or tie the weapon to a crime.

Recovering Weapon Serial Numbers Using Chemical Restoration

Chemical restoration is a type of chemical milling. It is used to slowly remove material to create the desired shape. In serial number restoration, small amounts of metal are removed until the serial number is brought back to the surface. This can be performed because of the depth that serial numbers are engraved into the weapon.

However, chemical restoration is limited by that depth and is only successful when the obliteration of the serial number is superficial. Examiners performing a restoration first sand the area where the serial number used to be. This removes any debris from the area left when an attempt was made to erase the serial number. The examiner then chooses a chemical, usually an acid, to slowly bring the number back to the surface. The type of chemical used depends on the material from which the weapon is made. The acids may range from Fry’s Reagent for a magnetic metal to an acidic ferric chloride solution for non-magnetic, non-aluminum metals. Fry’s Reagent is a mixture of hydrochloric acid, cupric chloride, and distilled water.

Forensics Examination of Spent Cartridges

Spent cartridges found at a scene can be examined for physical evidence such as fingerprints or compared to samples that match them to a weapon. The examination of the cartridge relies on the unique tool marks left by the various parts of the weapon including the firing pin and the ejector in a semi or fully automatic firearm. These markings can be compared and matched to known exemplars fired from the same weapon using the same parts.

The examination of the marks left on the cartridge is done using a comparison microscope. Examiners view the questioned cartridge and the known sample simultaneously, looking for similar microscopic marks left during the firing process.

Cartridges are also routinely examined for fingerprints because loading ammunition into the magazine or chamber leaves recoverable impressions if done so using bare hands. The fingerprints can survive the firing processes and while rare, fingerprints have been obtained from cartridges recovered from the scene.

To obtain the fingerprints, spent cartridges are subjected to cyanoacrylate fuming and carefully examined. Usable prints are photographed and may be uploaded to fingerprint databases such as IAFIS for comparison with known prints. Cartridges may also be swabbed for trace DNA left by the individual who loaded the magazine. The extremely low levels of recoverable DNA present the same issues as swabbing a firearm for DNA.

Microstamping Gun Firing Pins

Advancements in microscopic stamping have led to a push for the inclusion of firing pin microstamping. The microstamp is etched onto the firing pin and is transferred to the cartridge during the firing process. Each firing pin would have a unique serial number allowing investigators to trace casings found at a crime scene to a known firearm.

Microstamping is not in use nationally as of 2017, but the state of California enacted legislation in 2007 that requires microstamping on all newly sold firearms. The law and microstamping in general has received significant opposition from gun manufacturers because of the increased costs associated with introducing the microstamps on the manufacturing lines.

As of 2014, Smith and Wesson joined Ruger in a boycott of the state, pulling its weapons from shelves there. By 2016, the microstamping law in California had resulted in an inability for gun shops to sell new models. In addition, the National Shooting Sports Foundation launched a legal challenge to the law and in December 2016 the 5th Appellate District Court of Appeal ruled the lawsuit may proceed.

Opponents of the measure argue that microstamping will do little as a forensics tool and claim that the measure is only being introduced to further reduce weapons sales; microstamping is a highly-politicized concept.

Forensics Examination of Bullets

From its inception, ballistic forensics has examined bullets, matching these to the weapon used to fire the projectile. In modern forensics, there are two key methods for doing so:

  1. According to class characteristics
  2. According to individual characteristics

Examining the Class Characteristics of a Projectile

Preliminary examination of the bullet can exclude many weapons by examining the general characteristics of a recovered bullet. By determining general aspects of the fired ammunition, many guns may be immediately excluded as being incapable of firing that type of bullet. The make and model of the weapon can also be inferred from the combination of different class characteristics that are common to specific manufacturers.

The three main class characteristics of all bullets are

  • the lands and grooves
  • the caliber of the bullet, and
  • the rifling twist

All three characteristics can be tied directly to the type of barrel that was used to fire the bullet. The lands and grooves of the barrel are the bumps and valleys created when the rifling is created. The caliber is the diameter of the barrel. The twist is the direction of the striations left by the barrel’s rifling, clockwise (right-handed) or counterclockwise (left-handed). Most barrels will have a right-handed twist. One exception is weapons created by the Colt Manufacturing Company.

Weapon barrels that match the class characteristics of recovered bullets can be examined further for individual characteristics to determine the weapon from which the bullet was fired.

Examining the Individual Characteristics of a Bullet

To compare individual striations, examiners obtain a known sample using the seized weapon. This is done by firing the weapon into a soft target and recovering the slug.

For slower-traveling bullets, such as pistols or revolvers, known bullet exemplars are created by firing the weapon into a water tank. The spent bullet can be recovered intact because the water slows down the bullet before it can reach the tank walls.

For faster-traveling bullets, such as those fired from high-powered rifles and military style weapons, water tanks cannot be used because the tank will not provide enough stopping power for the projectiles. To examine these weapons, investigators must fire them at a target at a controlled range with enough backing to stop the bullet but not destroy it. The slug is then collected for examination.

Once a known sample is produced, it can be compared to the evidence by examining both at the same time using a comparison microscope. Striations that line up are examined more closely, looking for multiple consecutive matches. There is no set number of consecutive matches that equates to a match declaration but examiners are trained to use the phrase “sufficient agreement” when testifying. The degree to which an examiner can make that determination is based on their training and expertise.

All findings by examiners are subject to questioning by prosecution and defense attorneys during testimony in court.

Striation Databasing

Bullets and casings found at a scene require a known sample to compare to if they are to be matched to a weapon. Without a weapon, the striation pattern can be uploaded to a database such as the National Integrated Ballistic Identification Network (NIBIN) maintained by the ATF or the United Kingdom’s National Ballistics Intelligence Service (NABIS). Information uploaded to these databases can be used to track gun crimes and to link crimes together. Those who maintain these databases recommend that every recovered firearm be test fired and the resulting known exemplar be uploaded into the database.

Integrated Ballistics Identification System (IBIS)

The Integrated Ballistics Identification System (IBIS) is the brand of Automated firearms identification system manufactured by Forensic Technology WAI, Inc. of Montreal, Canada.

IBIS has been adopted as the platform of the National Integrated Ballistic Information Network (NIBIN) Program used by the United States Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF). NIBIN tracks about 100,000 guns used in crimes.

The integration of this technology into about 220 sites across the continental US and its territories facilitates sharing of information between different law enforcement groups. The rapid dissemination of ballistics information allows collection and tracking of gun-specific information to multiple crimes irrespective of geographic location. A National Research Council report has found that with the NIBIN database, a bullet retrieved from a crime scene will generate about 10 possible matches with about a 75-95% chance of a successful match.

Whereas some groups have advocated laws requiring all firearms sold be test-fired and registered in such a database, some oppose such a measure. In 2005, a Maryland State Police report recommended a law requiring all handguns sold in the state be registered in their IBIS system be repealed; in support of the repeal the MSP reported that the system, which costs taxpayers $2.5 million, had not produced “any meaningful hits”. The Maryland IBIS system was shut down in 2015.

Likewise, the CoBIS (Combined Ballistic Identification System) in New York state was shut down in 2012 because, according to the New York Post, the “program NEVER worked. Despite the hundreds of thousands of spent shells submitted, not one criminal was ever captured using the extensive and costly-to-maintain database, state officials concede.”

Source Links and Additional Materials

This article uses material from the Wikipedia article “Forensic_Firearm_examination”, which is released under the Creative Commons Attribution-Share-Alike License 3.0.