Chapter 16 Impressions and Ballistics 1 Impression Evidence

Chapter 16 Impressions and Ballistics 1

Impression Evidence Observable 3 D marks from contact with another object What can leave an impression? • Our fingers, hands, feet, teeth and even lips and ears • Weapon parts • Tires • Tools 2

Impression Evidence An object comes into contact with a soft or moldable substance to leave behind an exact imprint of the original object. • The image formed is a negative impression of the original object • Making a casting forms a positive of the original 3

Impression Evidence 4

Impression Evidence 5

Shoe Impressions 6

Shoe Impressions 1) Class Info learned: • manufacturer, • make • model of the footwear from the sole pattern. Greatly aided by databases, such as SICAR and Tread. Mark Note: Footwear impressions may often be individualized by identifying imperfections or unique wear patterns. 7

Impression Evidence 2) Determination of how many people and objects were involved in the incident 3) Description of the movements of the participants and objects (e. g. , weapons, vehicles, furniture, etc. ) 8

Impression Evidence 4) Establish a timeline and sequence of actions that occurred during an incident – what happened first, next, and so on 5) Support or refute eyewitness, suspect, and victim accounts of what occurred. 9

Impression Evidence Impressions can also be divided into three basic types • Visible impressions are those that are readily observable without any visualization aids. • Latent impressions are those that are not immediately observable but can be “developed” using a variety of techniques • Special light sources, chemical reagents, powders and spectroscopic techniques 10

Tire Marks Has both class and individual characteristics What class traits can we learn? • manufacturer, • model and • sometimes even the year of manufacture of a particular tire from its tread design. Individual wear traits: ex. Rocks, nails 11

Tool Marks Individualized Marks (e. g. striations) – Typical features (class characteristics) – Accidental of identifying features (individual char. ) - cuts, tears, gouges or other wear marks to individualize the tool. Rubber hoses cut by the same knife 12

Tool Marks: Preserving Evidence Silicone casting material 13

Dental/Bite Marks Dental Impression of gum, food, vicitms, etc. At Left: A. Chewing gum found at crime scene. B. dental impressions of victim and suspect. Unique root canal work of suspect found on gum. Also ABO blood type match. 14

Dental/Bite Marks Ted Bundy picked up for murder two sorority women at FSU using fake name and ID. One victim had bite marks on buttock. Casting of Bundy’s teeth taken (forcibly). Found to overlay (match) exactly the bite wound. Defended himself but convicted and sentenced to death. Before execution admitted to more than 40 other murders (but gave no info or details). 15

History of guns… It all began with the invention of gunpowder… • Discovered by Chinese alchemists sometime around the 9 th century and was used initially in fireworks to scare away evil spirits • Chinese had invented and begun using primitive versions of firearms by the early 13 th century • Early weapons were very crude and were referred to simply as “hand cannons” 16

Modern-day guns

Rifling Groove Land 18

Grooves and Lands put spin on bullet

Lands and Grooves create striations on bullet

• No two rifled barrels, even those manufactured in succession, will have identical striation markings Slight imperfections during rifling

Caliber • What is caliber?

Caliber • Diameter of gun barrel between opposite Lands • Recorded in hundredths of inch or millimeters • Ex: . 22 inch, . 38 inch, 9 mm • NOT exact • . 38 Cal may have barrel range of 0. 345 -0. 365

Bullet-Gun Connection Need bullet from crime scene and suspected gun Shoot gun to recover undamaged bullet

Bullet to Gun Comparison

Things to compare • Number of Land Groove Markings – A 5 Land/Groove bullet does not come from a 6 land gun – Width of Lands and Grooves • Direction of twist – A right twist bullet can’t come from a left twist barrel • Striation specifics

FBI General Rifling Characteristics Files

Problems Perfect Land/Groove Markings Reality: Frags, Grit, Rust

Why can’t we get striation markings from shotgun ammunition?

Shotgun Ammunition Weigh and measure diameter of shot pellets

Shotgun Small pellets 32

Shot

Shotguns and Gauges • What is a shotgun’s gauge?

Gauge • Diameter of barrel – Ex. 12 gauge=diameter of 0. 730 inches 16 gauge=diameter of 0. 670 inches

Ballistic Mechanics

Ballistic Mechanics 1. Trigger Pulled 2. Activates Firing Pin 3. Hits Primer

Ballistic Mechanics 4. Gunpowder ignited 5. Gases propel bullet through barrel 6. Spent casing bashed against breechblock Striations breechblock

Ballistic Mechanics 7. Spent Cartridge removed from barrel by an Extractor 8. Spent Cartridge thrown out of gun by the Ejector Both are sources for markings!

• Ammunition

• - Semi-Automatic Rifle or Shotgun

Gunpowder Residue • Why is it important to know the range of gun to victim?

Gunpowder Residue • Suicide (-at long range? ) • Self-defense (-but shot close & side of head? )

Gunpowder Residue

Shot Distance Determinations • • Need victim clothing with bullet holes Need the weapon Need identical clean clothing Need to fire shots at various distances at clean clothing to reproduce markings on clothes

Shot Distance Determinations Muzzle fire burns or melts cloths Concentrated burn marks and shot residue immediately around hole Close Range, less than 6”

Shot Distance Determinations Halo of smoke-soot around hole Shot 12” away

Shot Distance Determinations Scattered specks of shot residue with less soot around hole About 18” Away

Shot Distance Determinations • Weapon fired more than 3 feet from subject, no visible powder on subject • Can do a ”Bullet Wipe” – Around hole will be carbon, dirt, lubricant, primer residue and lead from bullet passing

Gunpowder Residues Soot is seen on the hand of a suicide victim, giving an indication that he was holding the weapon when it was fired. 51

Gunpowder Residues Modern smokeless gunpowder, and black powder, contains nitrate compounds. Black powder normally contains a combination of potassium nitrate (75%), charcoal (15%), and sulfur (10%). Smokeless powders can contain nitrocellulose (cellulose hexanitrate) as its main ingredient an also nitroglycerin (glycerol trinitrate). Gunpowder particulate residue around bullet entrance hole. 52

Determining the presence of powder residue on clothes • Greiss Test – Press a treated photo paper against questioned surface with an iron – Nitrate residue stuck and chemically enhanced • Lead Test – Spray Sodium Rhodizonate and then acids – Residue develops blue-violet color

Determining the presence of powder residue on hands Old School: Nitrate Test on hands Wax hands, lift wax Stain wax with diphenylalanine Get blue color Problem with false positives!

Determining the presence of powder residue on hands Detect: lead styphnate barium nitrate Antimony sulfide Swab hands to collect residue

Determining the presence of powder residue on hands • Atomic Detection Devices – Neutron Activation Analysis – Atomic Spectrophotometry – VERY Expensive technology!

Determining the presence of powder residue on hands • Collect samples from hands for Scanning Electron Microscopy • Problem with hours to scan for particles

Gunpowder Residues Scanning Electron Micrograph of GSR Diagram of the SEM-EDX pattern of GSR 58

Determining the presence of powder residue on hands • Overall Problem?

Determining the presence of powder residue on hands • Intentional and Unintentional washing off of residue • Have a 2 hr window to get accurate results.

Serial Numbers • Functions and Problems?

Serial Numbers • Stamped into metal • History of individual gun • ID Owner • Track crimes committed Can file down number!

Serial Number Restoration • Stamped metal area weaken • When acid is applied to filed area, the strained area will burn at a faster rate than surrounding metal

Firearm Collection NEVER PUT A PENCIL DOWN BARREL AREA! WHY?

• • Don’t want to disturb powder Don’t want to disturb rust and dirt Will destroy or alter future striation marks Unload gun and handle by trigger guard and grip area

Ammo Collection • Protect striations • Bullets in wall may become more damaged if removed improperly. • Wrap in paper • Put into pill box

Bullet Trajectory Analysis

Bullets-What influences trajectory? Tumbling dictates the injury pattern ("terminal ballistics”). – A short, high velocity bullet begins tumbling more rapidly in tissue. – A longer, heavier bullet might have more KE at a longer range when it hits the target, but it may penetrate so well that it exits the target witout much energy loss. – Even a bullet with a low energy bullet can impart significant tissue damage if it can be designed to give up all of its energy into the target (as with handguns). 70

Bullet Travel Bullets do not typically follow a straight line to the target. Rotational forces are in effect that keep the bullet off a straight axis of flight. 71

Firearms: Ballistics - the science of the travel of a projectile in flight. The flight path of a bullet includes: travel down the barrel, path through the air, and path through a target. 72

Firearms: Ballistics - – The controlled expansion of burning gunpowder generates pressure (force/area). – The area is the base of the bullet (equivalent to diameter of barrel) and is a constant. – The energy transmitted to the bullet will depend upon the bullet mass X force X the time interval over which the force is applied (function of barrel length). – Bullet travels through a gun barrel is characterized by increasing acceleration as the expanding gases push on it. The longer the barrel, the greater acceleration. Kinetic Energy (KE) = 1/2 MV 2 73

Integrated Ballistic Identification System (IBIS) In 1999, the formerly separate databases maintained by the FBI and ATF were merged together to form the National Integrated Ballistics Information Network, (NIBIN) • input and recover digital images of the markings found on fired bullets and cartridge cases either recovered from crime scenes or from test-fired weapons • digital images are then compared with those previously stored 74 • computer matching system

Databases IBIS DRUGFIRE