forensics - firearms unit. firearms murders by firearms became common in the 17 th century after...

Forensics - Firearms Unit

Firearms

• Murders by firearms became common in the 17th century after various wars placed such weapons in the hands of the peasant class.

• Many victims dies before anyone conceived of trying to match a gunshot to the person who fired it. Possibly the first recorded instance of this occurred in 1794 in county Lancashire, England

Firearms

• A wad of paper was discovered in the wound postmortem indicating a close shot.

• When the paper was opened, it was found to be a piece of a street ballad.

• When a suspect was arrested, authorities found the remainder of the ballad in his coat.

Firearms

• It matched the piece in the wound exactly.

• This convinced the jury of his guilt and they sentencing him to death.

• This began the important branch of criminalistics concerned with forensic firearms evidence.

Basic Arms & Ammunitionpg 85-88

• Firearms may be divided into two main categories: handguns & shoulder firearms

• Handguns (aka pistols) are designed to be held in the hand.

• Simplest type is single-shot pistol that must be loaded & cocked for each firing like the westerns when the cowboy had his hand on top of the gun with each shot


• Antique flintlock and percussion pistols are single shot pistols

• The .44-caliber Derringer pistol used to assassinate President Lincoln by John Wilkes Booth was a single shot percussion

• Other types of single shot pistols include certain models used for training or target shooting.


• Typical “zip guns”(homemade pistols), a clandestine “fountain-pen gun” & the sawed-off shotgun are single shot pistols

• Great majority of pistols today are multiple shot weapons, either revolvers or self loading pistols.

• Revolvers take their name from their revolving cylinder with multiple chambers to hold the cartridges

Revolver


• Most revolvers are 5 or 6 shot.

• With a single-action revolver, the cylinder turns to the next chamber each time the gun’s hammer is cocked by the thumb

• A double-action model doesn’t require manual cocking each time the trigger is pulled, the hammer is cocked.


• The cylinder revolves to the next position simultaneously & then is released firing the cartridge.

• A self-loading pistol a.k.a. auto loading or (erroneously) “automatic” takes cartridges from a magazine, sometimes (erroneously) called a “clip” which is located in the handle of the pistol

Semiautomatic


• This type of pistol may be fired as fast as the trigger is pulled & is often termed semiautomatic. A truly automatic pistol fires continuously while the trigger is held down.

• Unlike handguns, shoulder firearms have long barrels & are meant for use by both hands.


• The main types are rifles & smoothbore arms

• Rifles take their name from their rifled barrels. Rifling is a set of spiral grooves cut into the interior surface of the barrel.

• The raised areas between the grooves are called the lands.


• The latter bite into a bullet as it passes through the barrel & impart a spin or rotation to the bullet that results in a more stable trajectory.

• Rifles may be single-shot models, lever- or bolt-action magazine repeaters, or semi-automatic & automatic rifles.


• Lever or bolt-action magazine repeaters rely on manual handling of a lever or turn-bolt to extract & usually also eject the fired shell case, cock the firing mechanism, & move a new round into the chamber.

• Semiautomatic and automatic rifles work like their handgun counterparts


• Assault rifles such as the Soviet AK-47 & the American M-16 may be fired either in semiautomatic or automatic mode.

• Machine guns are fully automatic firearms that load their ammunition either from large magazines or belts & which due to their heave recoil are fired from a tripod or other mounting.


• In contrast, submachine guns are lighter & are intended to be hand held; they also fire pistol rather than rifle cartridges so they neither have the range nor the accuracy of automatic rifles.

• The caliber of a firearm originally referred to the diameter of the barrel bore.


• A .38-caliber is 38/100 inches. In countries using the metric system, the caliber is expressed in millimeters.

• Unlike rifles, shotguns have no rifling grooves so they are a type of smoothbore shoulder-fired weapon & are measured in gauges; the smaller the number, the larger the bore diameter.


• Shotguns may fire round balls or rifled bullets or much more commonly scatter shot.

• Shotguns may be single or double-barreled type that break down for reloading.


• Alternatively, there are repeating models that feed the shells from the magazine by pump action (or much less commonly with lever or bolt action) or that operate semi-automatically as with other semiautomatic weapons.


• A cartridge consists of a case made of brass (sometimes nickel-plated, to help prevent corrosion), filled with a propellant (black powder or smokeless powder), and fitted at the open end with a bullet (the projectile); the primer is a small explosive charge that sets off the propellant when it is struck by the firing pin.


• The primer may be located in an area around the outside circumference of the base, as in .22-caliber cartridges, in which case it is called rimfire ammunition. Almost all larger caliber ammunition is centerfire type – the primer is located at the center of the base.


• Bullets are usually made of lead or a lead alloy and my be jacketed (encased with a harder metal to help keep the bullet intact when it strikes a target) or semi-jacketed (encased only on the sides of the bullet or alternatively only at the nose.


• Soft-point & hollow-point bullets are semi-jacketed varieties intended to mushroom on impact. Other types of bullets may occasionally be encountered.

• Cartridge cases may be of three basic shapes:

– straight, tapered or bottlenecked


• Straight cases (straight-sided in profile; cylindrical); used for all .22-caliber rimfire cartridges as well as most handgun ammunition.

• Tapered cartridge cases (narrowing toward the top) are essentially obsolete.


• Bottleneck cases (having a sloping should area that reduces the case to a narrow diameter neck) are usually used for centerfire rifle cartridges because that form provides a much greater ratio of propellant to bullet caliber adding higher power.


• Shotgun ammunition is different from that of other firearms in several respects.

• Although formerly having full brass cases, shotshells are now made with brass bases to contain the primer and the remainder is made of heavy paper or plastic.

• A plain ball or rifled bullet may be inserted in the end of the case, with the bullet having fins or vanes that promote stability.


• Usually shotshells contain a quantity of shot, or round pellets, in sizes ranging from .05 inch for the number 12 or .33 inch for the number 00.

• The shot is separated by wads (discs of felt, paper, or the like) placed between the shot & the propellant & also over the shot to hold the charge in place & provide a proper seal.

Shotgun Shell Diagram

Shotgun Shell Slow Motion

Ballisticspg 88-91

• For a number of years this branch of investigation was referred to as forensic ballistics, but the use of this terminology should be discouraged.

• Ballistics is the science of the motion of projectiles, and one versed in this field is both a physicist & a mathematician

Ballisticspg 88-91

• The term forensic was intended to indicate that the expert’s ballistic knowledge was limited to the legal field.

• To avoid misrepresentation it is wise to refer to this science as Firearms Identification & to an individual working in the field as a Firearms Examiner or Firearms Identification Technician.

Ballisticspg 88-91

• Main types of ballistics: internal, external & terminal

• Internal ballistics deals with first, the forces that set the bullet in motion helping it to overcome inertia (the tendency of a body at rest to remain at rest or of a body in motion to keep moving) & second, the movement of the bullet through the barrel of the firearm.

Ballisticspg 88-91

• Interior ballistics also includes actions that take place before the powder charge is ignited. These include pulling of the trigger, fall of the hammer & explosion of priming mixture.

• During interior ballistics phase, markings are put on the shell case & bullet that will be the focus of any effort to match them with others.

Ballisticspg 88-91

• Exterior ballistics deals with the bullet’s trajectory-its flight from the time it leaves the barrel until it impacts the target.

• Inertia is involved because there is no driving force acting upon the bullet after it has left the barrel.

• Trajectory also involves the additional forces of gravity, velocity & yaw.

Ballisticspg 88-91

• Gravity begins a downward pull on a bullet as soon as it leaves a barrel; air resistance causes a slowing of any projectile

• Velocity is the speed of any portion of a bullet’s flight (first being muzzle velocity) and yaw, a tendency for a bullet to wobble as it first leaves the barrel usually corrected by the spin imparted to it.

Ballisticspg 88-91

Ballisticspg 88-91

• Terminal ballistics is how the projectile including shot, wad, etc. interacts with its target. Relevant forces include striking energy, penetration, and ricochet.

• Striking energy is the force exerted as a bullet hits the target

• Penetration is the depth to which the projectile traverses the target material

Ballisticspg 88-91

Ballisticspg 88-91

• Ricochet is a bullet’s glancing off an object that it strikes at an extreme angle.

• Ricochet “is, to the firearms examiner a very important ballistic factor”.

• The firearms examiner should always investigate a crime scene for the possibility of bullets having ricocheted.

Ballisticspg 88-91

• “Keyhole” defect (pg 91) – entrance wound is too small to have been caused by caliber weapon in question.

• These cases illustrate not only the terminal ballistics & related matters of physics involved, but they also demonstrate the need to keep an open mind and to conduct research and even experiments where warranted.

Identifying Characteristicspg 91-98

• In contrast to ballistics, the science of firearms examination is concerned primarily with issues of identification.

• In 1835, the first successful attempt was made to link a bullet (not wad as before) recovered from a murder victim’s body to a suspect in a crime. Henry Goddard was the investigator not related to Calvin Goddard


• In 1889 a French professor named Alexander Lacassagne sought to identify a murder bullet that had been fired through a rifled barrel & have seven resulting longitudinal grooves.

• The suspect was convicted of murder based on evidence. Today, this would be recognized as class evidence not fool proof individual evidence.


• The case in which crucial distinction between class & individual evidence took place in 1898.

• German chemist, Paul Jeserich received a bullet recovered from a man’s body murdered near Berlin. He fired a test bullet into soft material. Noticing similarities between it & the questioned bullet, he compared them under a microscope.


• On the basis of agreement between their markings, he testified that the fatal bullet was fired by the defendant’s revolver.

• Paris, May 1912, Victor Balthazard lectured at the Congress of legal medicine about a case in which he had testified.


• He used enlarged photographs to show some 85 points of correspondence between fatal bullets recovered in the case and test bullets fired from the defendant’s revolver.

• The evidence resulted in a conviction. His lecture was instrumental in “ballistics” being accepted as a legitimate branch of forensic science.


• As a bullet is propelled from a rifled barrel, one having the spiraling set of grooves & lands that constitute rifling, a series of parallel markings are imparted to it.

• These are the land impressions & groove impressions that constitute class characteristics and also certain parallel scratches.


• These striae or striations are result of imperfections in the bore-tiny flaws in the lands & grooves that are placed in the barrel both during manufacture & through subsequent use. The striae represent individual characteristics making it possible to match test bullets with one in question & demonstrate they came from the same firearm & excluding all others.

Firearms


• The class characteristics are useful in identify the type of weapon.

• The number of lands & grooves in firearms which vary from 2 to 22 can help in identifying the make & model, as can the widths of these impressions.


• The direction of spiral of the rifling is also important. (spin direction grooves are cut into the interior surface of the barrel to form lands and grooves)

• Rifling with a left-hand twist is often called “Colt-type rifling”, while that with a right-hand spiral is often referred to as “Smith and Wesson-type rifling”. The degree of twist occasionally may be useful as well.

Identifying Characteristics


• Once class characteristics of the test bullet are compatible with the questioned bullet, a comparison of the two is made with the comparison microscope.

• The following is how comparison of two bullets is done using a comparison microscope.


• Two bullets mounted; look at entire surface of rotating bullets at relatively low magnification for purpose of locating on one of the bullets the most prominent group of striations. Once marks are located, that bullet remains stationary.


• Examiner rotates other, or test bullet in an attempt to find corresponding area with individual characteristics that match those on the evidence bullet.

• If what appears to be a match is located, examiner rotates both bullets at the same time to determine whether or not similar coincidences exist on other portions of the bullets.


• Upon finding corresponding marks on other portions while having bullets in the same relative positions as when the first matches were observed, the examiner proceeds with further examinations of the same nature at higher magnification.


• A careful study of all the detail on both bullets ultimately permits the examiner to conclude that both bullets were or were not fired through the same barrel.

• The comparison may be recorded on one or more photomicrographs.


• Caution: Even if bullets were fired in succession from the same weapon, not all individual characteristics would be identical. There would be some striations caused by powder residues, sand or dirt, rust, corrosion & pitting, & other surface factors or “fugitive” materials which are not likely to be duplicated on all bullets fired through that particular barrel.


• There may be other striations such as marks on metal-cased bullets due to imperfections on the interior of the sizing die used in the fabrication of the bullet.

• Fired bullets might contain crimp or burr impressions left there by the mouth of the cartridge case or shell. Presence or absence of marks must be discounted by firearms identification technician.


• Entire process is laborious & painstaking. Welcome to the new state-of-the-art computer systems and software that enable crime labs to trace bullets & shell casings through the recognition of their identifying characteristics such as “Bulletproof” & “Drugfire” which function as sorting aids instead of taking over work of the expert.


• The Bulletproof database can store & retrieve data on three hundred thousand bullets & compare 55 thousand in under two hours that would require years the manual method. It is estimated it can do the work of 55 firearms technicians.

• In collecting firearms evidence, care should be taken not to place accidental markings on soft lead bullets (no forceps)


• Also, no foreign object should ever be inserted in the barrel of a gun (if trying to avoid fingerprints). This may scratch the inside of the barrel, thus altering the striation evidence that will subsequently be produced on test bullets.

• Tissue, blood, fibers or other trace evidence may be dislodged as well.


• Shell identification is much less useful that bullet identification for two reasons:

• Unless a shell case was discovered at the crime scene, the proof it came from a particular gun can have little value

• The fact a shell is at a crime scene doesn’t prove as a bullet does the firearm it came from was the one used in the crime.


• Firing pin indentations are produced when the firing pin is struck by the hammer and forced into the primer leaving a crater.

• Breech face markings are caused by the burning gases inside the casing forcing the cartridge back against the weapon’s breach face. Any striations on the breach face are recorded on the shell.


• In semiautomatic & automatic firearms, extractor markings & ejector markings are left by the respective mechanisms on the rim of the shell case.

• Also, the magazine may leave marks on the side of the cartridge & depending on the firearm, certain additional markings may be imparted to the shell case as the result of some particular mechanism.


• Sometimes firearms are recovered with their serial numbers ground off to conceal the owner’s identity.

• If the grinding has not been excessively deep, the numbers can usually be restored by the examiner.


• Restoration depends on the fact that the underlying metal crystals are placed under a strain when the numbers are stamped into the firearm’s frame.

• When an etching agent is applied, the strained area will dissolve faster than the surrounding metal, permitting the pattern of stamped numbers to appear & be promptly photographed.


• Other manufactured items, including engine blocks of automobiles, may also have serial numbers that require restoration.

• Depending on the metal, other techniques such as heating or electrochemical etching may be effective.

Firearm Residuespg 99-101

• The explosion that occurs when a firearm is discharged produces two types of trace evidence: gunshot residues & powder pattern deposits

• Gunshot Residue Analysis – GSR particles are usually deposited on the hand or hands of the person firing a gun


• These may adhere for up to 6 hours or so, but may also be removed by washing or wiping of hands.

• They are present in greatest concentration immediately after the shooting, usually in the web area between the thumb & forefinger (index finger).


• Three methods of GSR testing & two methods of collection.

• Testing: neutron activation analysis (NAA) or atomic absorption spectrophotometry (AA), evidence is collected by using cotton-tipped plastic swabs (wood contains substances that interfere with the test). 5% Nitric acid solution sprayed on hands & then swabbed twice.


• For testing by scanning electron microscopy/energy dispersive x-ray analysis (SEM/EDX), small aluminum discs to which double-sided cellophane tape is affixed are used for collection.

• The adhesive is pressed on the top of the webbed portion of each hand.

Firearm ResiduesSEM GSR

Firearm ResiduesSEM/EDX GSR


• Negative result may mean that a subject either did not fire a weapon or took some action that resulted in removal of any particles that had been present.

• Positive result means that the subject fired a weapon sometime during the past 6 hours (approximately), or handled a weapon during that time period.


• Location of the particles is of importance.

• If the palms, but not the backs, of a subject’s hands contain GSR, this might indicated that the person held but did not fire a weapon or that the weapon was relatively “clean”, meaning it gave off a small amount of GSR particles when fired.


• The old “paraffin test” or “dermal nitrate test” is no longer recommended because it lacks specificity & common materials such as urine, tobacco, cosmetics, & fertilizer give false positive results.

• Powder pattern deposits may include burned & unburned particles of lead, barium, gunpowder, nitrates & other chemicals


• When a firearm is discharged at relatively close range, gunpowder & other materials may be spewed onto the target.

• Factors such as the type of gun & length of barrel as well as type of ammunition will affect powder pattern in size & density.

• Appearance of pattern may help indicate distance between firearm & target.

Contact

Contact with Abrasion

Intermediate ContactPowder Tattooing

Exit Wound

Entrance Exit Wound

• Entrance at the left & exit at the right. This bullet struck at an angle to produce the ovoid entrance. There may be no exit wound at all if the bullet's energy is absorbed by the tissues. Some bullets (such as a "hollow point") are designed to deform so that all their energy will be converted to tissue damage & not exit.


• If weapon is fired a half inch or closer to the target, there usually is no powder pattern.

• Tests with same firearm & ammunition fired into heavy paper or cardboard at varying distances should give a range of patterns that can be compared to evidence to estimate distance.


• If weapon hasn’t been recovered, best the examiner can do is state whether or not a shot could have been fired within the same distance interval from the target.

• In case of clothing, the surface should be examined microscopically for traces of powder deposits.


• Sometimes, because of the color of the clothing or the presence of blood, the particles of deposit will not be apparent.

• In such cases an infrared photograph may overcome the problem, or chemical tests may be used to detect the chemical residues.

The Sacco & Vanzetti TrialCase Study pg 101-108

• April 15, 1920: robbery happened about 40 miles from Salem, Massachusetts with payroll clerk & guard being shot & killed by two men who made off with both bags of money.

• Supposedly a third man who didn’t fire shots but was driving getaway car.


• Getaway car found abandoned in wooded area. When owner came to get it, he fled seeing the police but left the two men with him who were later apprehended.

• Suspects matched descriptions given: clean shaven factory worker Nicola Sacco, age 29, and heavily mustached 32 year old Bartolomeo Vanzetti.


• Both were Italian immigrants & away from homes in Plymouth; both armed illegally.

• Vanzetti’s shotgun shells were similar to ones left at scene of payroll robbery.

• Suspects were in possession of “anarchist literature”. About 60 witnesses for prosecution & about 100 for the defense.


• Firearm evidence was damaging for the defense.

• While all firearms testimony came from men who had certain knowledge of arms & ammunition, It was clear none of them had training as firearms examiners.

• Jurors wanted magnifying glasses so they could examine bullet themselves.


• Jury concluded that the fatal bullet had indeed been fired from Sacco’s pistol.

• Jury found the defendants guilty of murder in the first degree, & they were sentenced to execution.

• Death sentence was in reality the beginning of a 7 year period of controversy rather than being the conclusion to a case.


• Demonstrations were held around the world.

• Requests for their release came from different countries also.

• Around the world, American embassies were bombed & U.S. officials threatened.

• Supposedly the Mafia (Morelli brothers) were said to have robbed the shoe factory payroll.


• 1927 Calvin Goddard got involved in the case. His evidence proved Sacco’s pistol did not fire the first or second bullet from the murder scene. Third bullet did come from Sacco’s gun.

• Fatal bullet was proven conclusively to have been fired from Sacco’s gun.


• From this time forward, forensic ballistics became a new type of judicial proof which ruled out mere opinion.

• On August 23, 1927, while millions of sympathizers protested worldwide, Nicola Sacco & Bartolomeo Vanzetti were executed along with another death-row inmate by electric chair soon after midnight that Tuesday morning.


• Vanzetti forgave those who, he still maintained, were executing an innocent man.

• Sacco, who had preceded him in death was defiant to the end, condemning the social order that punished him.

• Three decades later, again the evidence was examined with the same conclusion.


• The case had already become a legend.

• Sacco and Vanzetti will be remembered as folk heroes in the fight for freedom rather than the brutal killers who murdered for gain.

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