Firearms tool marks and other impressions
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FIREARMS, TOOL MARKS, AND OTHER IMPRESSIONS. Forensic Science - Chapter 16. Famous People Killed / Wounded with Guns.

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Firearms tool marks and other impressions

FIREARMS, TOOL MARKS, AND OTHER IMPRESSIONS

Forensic Science - Chapter 16


Famous people killed wounded with guns

Famous People Killed / Wounded with Guns

  • Abraham LincolnJohn LennonJohn F. KennedyRobert F. KennedyMartin Luther King Jr.Pope John Paul llMohandas GhandiFranz FerdinandMalcolm XBob MarleyRonald ReaganTheodore Roosevelt50 CentThe Notorious B.I.G.Tupac ShakurSean Taylor


Introduction

Introduction

  • Structural variations and irregularities caused by scratches, nicks, breaks, and wear may permit the criminalist to relate:

    • A bullet to a gun

    • A scratch or abrasion mark to a single tool

    • A tire track to a particular automobile

  • Video part 1 Video Part 2 Video part 3

  • Individualization, a goal of in all areas of criminalistics, frequently becomes an attainable reality in firearm and tool mark examination.


Father of ballistics

Father of Ballistics

  • Calvin Goddard, physician , acquired data from all known gun manufacturers in order to develop a comprehensive database.

  • Video FBI


Charles waite

Charles Waite -

  • Goddard his partner, Charles Waite, he catalogued the results of test-firings from every type of handgun made by 12 manufacturers. Waite also invented the comparison microscope. With this instrument, two bullets could be laid adjacent to one another for comparative examination.


Terminology of guns

TERMINOLOGY OF GUNS

  • Due to the multiple types, purposes, and cultures that have developed around firearms, a language of its own has developed. Before discussing the forensics of firearms, one must have a grasp on the terminology associated with guns.

  • We will look at different types of guns and their parts and uses.


Types of guns

TYPES OF GUNS

  • Modern firearms are manufactured in a variety of shapes and sizes to fit multiple purposes.

  • These include semi-automatic and even automatic weapons built primarily for military usage. Virtually any type of gun

  • can be found on the streets in use by youth gangs, persons involved in drug trafficking, "survivalists", and even what we would consider "ordinary" citizens.


Handguns

HANDGUNS

  • Ahandgun was conceived as a compact weapon for self defense.

  • The two most common defensive handguns

    are the double action revolver and the semiautomatic pistol.


Revolvers

REVOLVERS

  • The revolver is the older type of handgun. It is less expensive, easy to use, simpler in design, and more reliable than semiautomatics.

  • However, compared to semiautomatic weapons, revolvers are limited to six shots, relatively slow to reload, less efficient, and the trigger pull is more difficult.


Revolvers1

Revolvers

  • The revolver, the first multiple shot

  • hand gun, has several advantages they are less expensive, simpler in design, and more

  • reliable than semiautomatics. A revolver is

  • easy to use and are accurate.

  • However, compared to semiautomatic weapons, revolvers are limited to six shots, relatively slow to reload, less efficient, and the trigger pull is more difficult.


Handguns revolver

HandgunsRevolver


Parts of a handgun

Parts of a Handgun


Revolvers parts

Revolvers Parts

  • If the barrel length is shorter, for ease of concealment, the gun becomes less accurate in hitting the target.

  • An ejector rod under the barrel is used to eject fired cartridges from the open cylinder before reloading.

  • The sights, which are lined up when aiming the weapon, on a revolver are usually a blade in the front and a notch on the rear.


Revolver parts continued

Revolver Parts Continued

  • The frame is the largest part, and all other pieces attach to it. Frames are usually made of blued or plated steel, stainless steel, or lightweight alloys such as magnesium. The cylinder contains five or six holes for the cartridges and can be swung out for reloading. This must performed manually; the absence of cartridge cases at a crime scene may indicate the use of a revolver.


Parts of revolver continued

Parts of Revolver Continued

  • On a revolver, there is a gap between the cylinder and barrel to allow the cylinder to turn freely, this also allows gases and gun powder residue to escape laterally and allow the forensic pathologist to predict the location of a shooter more easily.

  • The inner mechanics of a revolver uses the energy from a trigger pull to rotate the cylinder, cocking the weapon, and then fall the hammer.


Revolver parts continued1

Revolver Parts continued

Revolver with cylinder out for reloading

Old Wild West Colt 45


Revolver firing mechanism

Revolver Firing Mechanism

  • Revolvers can have one of two distinct

  • firing action designs. A single-action

  • revolver, the oldest and simplest action,

  • requires a shooter to cock the hammer back

  • before each pull of the trigger. SLOW.

  • In a double-actionweapon, a trigger pull will cock the weapon manually and fire the gun. This requires quite a bit more pressure and may compromise accuracy.


Semiautomatic pistol

Semiautomatic Pistol

  • A more recent development than the revolver the pistol originated in the late 19th century. The advantages of semiautomatics stem from the use of recoil generated by the fired cartridge to eject the empty cartridge case, load the next cartridge, and cock the hammer.

  • This is more conducive to firing

  • multiple shots at multiple speeds. Many pistols are designed to carry 15 to 19 rounds.


Handguns semi automatic

HandgunsSemi-automatic

Courtesy of C. Fanning

Courtesy of C. Fanning

Courtesy of C. Fanning


Semiautomatic pistol disadvantes

Semiautomatic Pistol Disadvantes

  • Disadvantages:

  • A more complicated mechanism requires more practice to use accurately, and is more likely to malfunction.

  • In addition, cartridge cases must be shorter to work well; because of this revolver cartridges are more powerful than semiautomatic cartridges.


Parts of a semi auto handgun

Parts of a Semi-auto Handgun


Parts of a semi auto pistol

Parts of a Semi-auto Pistol


Rifle types

Rifle Types

  • Rifles differ from handguns in the length of the barrel and the presence of a butt stock.

  • They are harder to carry, are poorly concealable, and more loosely regulated than handguns.

  • However, they are much more accurate and shoot more powerful cartridges than handguns. Rifles may be manufactured as

  • single shot; but, most commonly rifles possess bolt action, like. Military rifles are semiautomatic or automatic, having a detachable magazine holding 5 to 50 rounds.


Rifle types1

Rifle Types

Old Fashion Lever type rifle.

Bolt action hunting rifle

Semi-automatic hunting rifle


Muzzleloading rifle

Muzzleloading Rifle


Parts of a bolt action rifle

Parts of a Bolt Action Rifle


Automatic rifles

AUTOMATIC RIFLES

  • Automatic weapons are those weapons which will fire repeated rounds when the trigger is pulled and held. This allows the weapon to fire, reload and fire again as fast as the gun can possibly move. The most widely know automatic weapons are machine guns.

  • Most of these weapons are not legal, for personal use. It is possible for a skilled gunsmith to convert a semiautomatic

  • into a fully automatic weapon.


Parts of a semiautomatic rifle

Parts of a Semiautomatic Rifle

M1 carbine will fire each time you pull the trigger without manually reloading. The shells are held in the vertical clip under the receiver.


Assault weapons

ASSAULT WEAPONS

  • Assault weapons are those weapons designed to kill mass numbers of people at a time.

  • The classification includes automatic weapons, machine guns, sawed off shotguns, grenade

  • launchers, and many other weapons used by the military.


Automatic assault rifles

Automatic Assault Rifles

The most deadly gun that is commonly hand carried by the shooter. It can fire many rounds without reloading; as fast as you can pull the trigger and can be set to fully automatic mode.


Ballistic fingerprinting

Ballistic Fingerprinting

  • Ballistic fingerprinting refers to a set of forensic techniques that rely on marks that firearms leave on bullets to match a bullet to the gun it was fired with.

Video – Ohio State forensics Class


Gun barrel markings

Gun Barrel Markings

  • The inner surface of the barrel of a gun leaves its markings on a bullet passing through it.

  • These markings are peculiar to each gun.

  • The gun barrel is produced from a solid bar of steel that has been hollowed out by drilling.

  • The microscopic drill marks left on the barrel’s inner surface are randomly irregular and serve to impart a uniqueness to each barrel.


Bullet recovery tank

Bullet Recovery Tank

  • Each gun submitted is test fired and the recovered bullets and cartridge cases are retained for use in further analysis.


Recovered bullets

Recovered Bullets

Video

Alias Forensics video


The bore of guns

The Bore of Guns


Gun barrel markings1

Gun Barrel Markings

  • The manufacture of a barrel also requires impressing its inner surface with spiral grooves, a step known as rifling.

  • The surfaces of the original bore remaining between the grooves are called lands.

  • The grooves serve to guide a fired bullet through the barrel, imparting a rapid spin to insure accuracy.


Riflings in a barrell

Riflings in a Barrell

Riflings are the groves that cause a bullet to spin and gain stability for a more accurate shot


Lands and grooves

Lands and Grooves

Land

Diameter

Caliber

Groove


Gun barrel markings2

Gun Barrel Markings

  • The diameter of the gun barrel, measured between opposite lands, is known as caliber. Most older guns’ calibers are measured in fraction of inches across the islands. So a 45 caliber bullet is 0.45 inches across. Some newer bullets are measured in millimeters.

  • Once a manufacturer chooses a rifling process, the class characteristics of the weapon’s barrel will remain consistent, each will have the same number of lands and grooves, with the same approximate width and direction of twist.


Striations

Striations

  • Striations, which are fine lines found in the interior of the barrel, are impressed into the metal as the negatives of minute imperfections found on the rifling cutter’s surface, or they are produced by minute chips of steel pushed against the barrel’s inner surface by a moving broach cutter.

  • These striations form the individual characteristics of the barrel.


Bullet striations from the barrel

Bullet Striations from the Barrel

The striations on the bullet can make identifiable and unique markings that trace it back to a particular firearm.


Striations1

Striations

  • It is the inner surface of the barrel of a gun that leaves its striation markings on a bullet passing through it.

Courtesy of C. Fanning


Bullet examination

Bullet Examination

  • No two rifled barrels, even those manufactured in succession, will have identical striation markings.

  • The number of lands and grooves and their direction of twist are obvious points of comparison during the initial stages of an examination between an evidence bullet and a test-fired bullet.

  • Any differences in these class characteristics immediately serve to eliminate the possibility that both bullets traveled through the same barrel.


The comparison microscope

The Comparison Microscope

  • The comparison microscope serves as the single most important tool to a firearms examiner.

  • Two bullets can be observed and compared simultaneously within the same field of view.

  • Not only must the lands and grooves of the test and evidence bullet have identical widths, but the longitudinal striations on each must coincide.


Comparison of bullet marks

Comparison of Bullet Marks


Calibers of bullets

Calibers of Bullets


Caliber of gun bores

Caliber of Gun Bores


Machine guns

Machine Guns

Fully automatic machine guns can fire up to 1200 bullets per minute.


Rapid fire machine gun

Rapid Fire Machine Gun

Typical cyclic rates of fire are 500–900 RPM for assault rifles, 900-1,200 RPM for submachine guns and machine pistols, and 600-1,200 RPM for machine guns. M134


Shotguns

SHOTGUNS

  • Shotguns have a similar external appearance to rifles, but differ in the lack of rifling

  • inside the barrel, which is the basis for their legal definition. A shotgun shell may contain one large projectile (called a slug), a few pellets of large shot, or many tiny pellets. Shotguns are available in single shot (break action), double barrel, pump action, and semiautomatic. Unlike rifled firearms, a shotgun has a smooth barrel.


Shotguns1

Shotguns

  • Shotguns have a similar external appearance to rifles, but differ in the lack of rifling inside the barrel, which is the basis for their legal definition

  • Unlike rifled firearms, a shotgun has a smooth barrel.

  • Shotguns generally fire small lead balls or pellets that are not impressed with any characteristic markings that can be related back to the weapon.


Shotguns gauge

SHOTGUNS - GAUGE

  • The diameter of the shotgun barrel is expressed by the term gauge. In the lower numbered gauges, it is the number of pellets that are needed to span the internal barrel diameter.

  • The higher the gauge number, the smaller the barrel’s diameter.


Shotguns2

SHOTGUNS

  • The truly unique thing about shotguns stems from the shot that is projected from the

  • barrel and the distribution patternas it approaches a target. The original intent of such a design was to lesson the skill needed to shoot small moving food targets, such as birds and rabbits.

  • Although these guns are still commonly used for such purposes, criminals, gangs, and even law enforcement uses them.


Shotgun shells

Shotgun & Shells


Shotgun impact patterns

Shotgun Impact Patterns

  • The firing distances involving shotguns must again be related to test firing.

  • The muzzle to target distances can be established by measuring the spread of the discharged shot.


Reloading shotguns

Reloading Shotguns

Semi-automatic ejection out the side of the reciever

Breechloading


Firing a weapon

Firing a Weapon

  • The act of pulling the trigger serves to release the weapon’s firing pin, causing it to strike the primer, which in turn ignites the powder.

  • The expanding gases generated by the burning gunpowder propel the bullet forward through the barrel, simultaneously pushing the spent cartridge case or shell back with equal force against the breechblock.

Video of Forensic Ballistics


Firing a weapon1

Firing a Weapon

  • The shell is impressed with markings by its contact with the metal surfaces of the weapon’s firing and loading mechanisms.


Anatomy of a shell

Anatomy of a Shell


Cartridge case comparison

Cartridge Case Comparison

  • The firing pin, breechblock, and ejector and extractor mechanism also offer a highly distinctive signature for individualization of cartridge cases.

Courtesy of C. Fanning


Cartridge case comparison1

Cartridge Case Comparison

  • The shape of the firing pin will be impressed into the relatively soft metal of the primer on the cartridge case.

  • The cartridge case, in its rearward thrust, is impressed with the surface markings of the breechblock.


Cartridge case comparison2

Cartridge Case Comparison

  • Other distinctive markings that may appear on the shell as a result of metal to metal contact are caused by the:

    • Ejector, which is the mechanism in a firearm that throws the cartridge or fired case from the firearm.

    • Extractor, which is the mechanism in a firearm by which a cartridge of a fired case is withdrawn from the firing chamber.

    • Magazine or clip, which is the mechanism that in a firearm holds the bullets.


Computerized imaging

Computerized Imaging

  • The advent of computerized imaging technology has made possible the storage of bullet and cartridge surface characteristics in a manner analogous to automated fingerprint files.


Computerized imaging1

Computerized Imaging

  • The National Integrated Ballistics Information Network, NIBIN, produces database files from bullets and cartridge casings retrieved from crime scenes or test fires from retrieved firearms, often linking a specific weapon to multiple crimes.

  • It is important to remember, however, that the ultimate decision for making a final comparison will be determined by the forensic examiner through traditional microscopic methods.


Nibin

NIBIN


Gunpowder residue

Gunpowder Residue

  • When a firearm is discharged, unburned and partially burned particles of gunpowder in addition to smoke are propelled out of the barrel along with the bullet toward the target.

  • If the muzzle of the weapon is sufficiently close, these products will be deposited onto the target.

  • The distribution of gunpowder particles and other discharge residues around a bullet hole permits an assessment of the distance from which a handgun or rifle was fired.


Gunpowder residue1

Gunpowder Residue

  • The precise distance from which a handgun or rifle has been fired must be determined by means of a careful comparison of the powder-residue pattern located on the victim’s clothing or skin against test patterns made when the suspect weapon is fired at varying distances from a target.

  • By comparing the test and evidence patterns, the examiner may find enough similarity in shape and density upon which to base an opinion as to the distance from which the shot was fired.


Gunpowder residue detection

Gunpowder Residue Detection


Gunpowder residue2

Gunpowder Residue

  • In cases where the weapon is held in contact with or less than 1 inch from the target, a star-shaped (stellate) tear pattern around the bullet hole entrance, surrounded by a rim of a smokeless deposit of vaporous lead is usually present.

  • A halo of vaporous lead (smoke) deposited around a bullet hole is normally indicative of a discharge of 12 to 18 inches or less. This deposits on the hands of a shooter and can be chemically analyzed for proof of shooting a gun.


Gun powder residue around wounds

Gun Powder Residue around Wounds


Gunpowder residue3

Gunpowder Residue

  • The presence of scattered specks ofunburned and partially burned powder grains without any accompanying soot is often observed at distances up to 25 inches (and occasionally as far as 36 inches).

  • More than 3 feet, will usually not deposit any powder residues, and the only visual indication is a dark ring around the hole, known as a bullet wipe.


Gunpowder residue4

Gunpowder Residue

  • When garments or other evidence relevant to a shooting are received in the crime laboratory, the surfaces of all items are first examined microscopically for the presence of gunpowder residue.

  • Chemical tests, such as the Greiss test, may be needed to detect gunpowder residues that are not visible. Atomic Absorption spectroscopy is also used to prove the presence of gun powder residue.


Griess test

Griess Test

  • The Griess test is a chemicalanalysis test which detects the presence of organicnitrite compounds. The Griess diazotization reaction on which the Griess reagent relies was first described in 1858 by Peter Griess.


Powder residue on clothing

Powder Residue on Clothing


Primer residue on hands

Primer Residue on Hands

  • The firing of a weapon not only propels residues toward the target, but gunpowder and primer residues are also blown back toward the shooter.

  • As a result, traces of these residues are often deposited on the firing hand of the shooter, and their detection can provide valuable information as to whether or not an individual has recently fired a weapon.


Primer residue on hands1

Primer Residue on Hands

  • Examiners measure the amount of barium and antimony on the relevant portion of the suspect’s hands, such as the thumb web, the back of the hand, and the palm.


Primer residue on hands2

Primer Residue on Hands

  • They may also characterize the morphology of particles containing these elements to determine whether or not a person has fired, handled a weapon, or was near a discharged firearm.


Serial numbers

Serial Numbers

  • Serial numbers are used to trace the ownership of a gun to a suspect or source. Increasingly, the criminalist is requested to restore a serial number when it has been removed or obliterated by grinding, rifling, or punching.

  • Restoration of serial numbers is possible through chemical etching because the metal crystals in the stamped zone are placed under a permanent strain that extends a short distance beneath the original numbers.


Serial numbers on guns

Serial Numbers on Guns


Firearm evidence collection

Firearm Evidence Collection

  • Firearms are collected by holding the weapon by the edge of the trigger guard or by the checkered portions of the grip.

  • Before the weapon is sent to the laboratory, all precautions must be taken to prevent accidental discharge of a loaded weapon.

  • In most cases, it will be necessary to unload the weapon.


Firearm evidence collection1

Firearm Evidence Collection

  • When a revolver is recovered, the chambers, their positions, and corresponding cartridges must be recorded.

  • Firearm evidence must be marked for identification (usually a tag on the trigger guard) and a chain of custody must be established.


Firearm evidence collection2

Firearm Evidence Collection

  • Bullets recovered at the crime scene are scribed with the investigator’s initials, either on the base or the nose of the bullet.

  • The obliteration of striation markings that may be present on the bullet must be scrupulously avoided.

  • The investigator must protect the bullet by wrapping it in tissue paper before placing it in a pillbox or an envelope for shipment to the crime laboratory.


Firearm evidence collection3

Firearm Evidence Collection

  • Fired casings must be identified by the investigator’s initials placed near the outside or inside mouth of the shell.

  • Discharged shotgun shells are initialed on the paper or plastic tube remaining on the shell or on the metal nearest the mouth of the shell.


Different tools guns

Different Tools / Guns

Tools of all types will leave marks that can be traced back to a source in criminal forensics.


Tool marks

Tool Marks

  • A tool mark is considered to be any impression, cut, gouge, or abrasion caused by a tool coming into contact with another object.

  • A careful examination of the impression can reveal important class characteristics, such as the size and shape of the tool.


Tool marks1

Tool Marks

  • But it is the presence of any minute imperfections on a tool that imparts individuality to that tool.

  • The shape and pattern of such imperfections are further modified by damage and wear during the life of the tool.


Tool marks2

Tool Marks

  • The comparison microscope is used to compare crime-scene toolmarks with test impressions made with the suspect tool.

  • When practical, the entire object or the part of the object bearing the tool mark should be submitted to the crime laboratory for examination.


Tool marks3

Tool Marks

  • Under no circumstances must the crime scene investigator attempt to fit the suspect tool into the tool mark.

    • Any contact between the tool and the marked surface may alter the mark and will, at the least, raise serious questions about the integrity of the evidence.


Tool marks on bones

Tool marks on bones

Tool marks on bones can identify the type of tool that was used in the crime and may isolate it down to individual evidence for a trial.


Other impressions

Other Impressions

  • Impressions of other kinds, such as shoe, tire or fabric impressions, may be important evidence.

  • Before any impression is moved or otherwise handled, it must be photographed (including a scale) to show all the observable details of the impression.

  • If the impression is on a readily recoverable item, such as glass, paper, or floor tile, the evidence is transported intact to the laboratory.


Footprints and tire marks

Footprints and Tire Marks


Other impressions1

Other Impressions

  • If the surface cannot be submitted to the laboratory, the investigator may be able to preserve the print in a manner similar to lifting a fingerprint.


Other impressions2

Other Impressions

  • When shoe and tire marks are impressed into soft earth at a crime scene, their preservation is best accomplished by photography and casting.

  • In areas where a bloody footwear impression is very faint or where the subject has tracked through blood leaving a trail of bloody impressions, chemical enhancement can visualize latent or nearly invisible blood impressions.


Points of comparison

Points of Comparison

  • A sufficient number of points of comparison or the uniqueness of such points will support a finding that both the questioned and test impressions originated from one and only one source.

  • New computer software and web sites may be able to assist in making shoe print and tire impression comparisons.

  • Also, bite mark impressions on skin and foodstuffs have proven to be important evidence in a number of homicide and rape cases.


Bitemarks and computer analysis

Bitemarks and Computer Analysis


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