Forensics Ch 9 Review (Firearms, Tool Marks & Other Impressions)

12, 18

A halo of vaporous lead (smoke) deposited around a bullet hole normally indicates a discharge _____ to _____ inches from the target.

smooth

A shotgun has a(n) _____ barrel.

individual

A wear pattern, cut, gouge, or other damage pattern can impart ____ characteristics to a shoe.

tool mark

A(n) ____ is any impression caused by a tool coming into contact with another object.

infrared

A(n) _____ photograph may help visualize gunpowder deposits around a target.

electrostatic lifting device

An imprint may be lifted using lifting sheets or a(n) _____.

yard

As a rule of thumb, the spread in the pattern made by a 12-gauge shotgun increases 1 inch for every ____ of distance from the target.

The firing pin, breech face mark, and ejector and extractor mechanism

Besides the barrel, what parts of a firearm may leave distinctive markings on a shell cartridge?

*Prior to unloading revolver, Ben should have noticed chamber position in line with the barrel & marked the position with a scratch on the cylinder. *Diagram of revolver should have been made and each chamber is designated with a number on the diagram. As each cartridge or casing is removed, it should be marked to correspond to numbered chambers in the diagram. *Each removed cartridge should be placed in separate envelope. *Instead of putting tag on grip of revolver, tag should have been applied on trigger guard. *To avoid deforming the bullet, pliers shouldn't have been used to draw the bullet out of the wall. The surrounding portion of the wall should be broken and bullet should be removed without any direct contact. *Bullet should have been wrapped in tissue paper before placing in the evelope.

Criminalist Ben Baldanza is collecting evidence from the scene of a shooting. After locating the revolver suspected of firing the shots, Ben picks the gun up by the grip, unloads it, and places the ammunition in an envelope. He then attaches an identification tag to the grip. Searching the scene, Ben finds a bullet lodged in the wall. He uses pliers to grab the bullet and pull it from the wall, then inscribes the bullet with his initials and places in an envelope. What mistakes, if any, did Ben make in collecting this evidence?

primer

Current methods for identifying a shooter rely on the detection of ____ residues on the hands.

Serial numbers can be restored because metal crystals in the stamped zone are placed under a permanent strain that extends a short distance beneath original numbers. When suitable etching agent is applied, strained area dissolves faster than the unaltered metal, thus revealing the etched pattern in the form of the original numbers. If the zone of strain has been removed, or if the area has been impressed with a different strain pattern, the number usually cannot be restored. Before any treatment with etching reagent, obliterated surface must be thoroughly cleaned of dirt/oil and polished to mirrorlike finish. Regeant is swabbed onto surface with cotton ball. Solution of HCL, CuCl, and water work well for steel surfaces.

Describe how a criminalist restores an obliterated serial number on a weapon.

Examiner will test-fire the weapon into a tank and recover the bullet. Bullet will be compared to the suspect bullet. 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 also the longitude striations on each side must coincide. There is no minimum number of points required for a bullet comparison. The final opinion must be based on the judgment, experience, and knowledge of the expert.

Describe how a firearms examiner compares two bullets. What characteristics does an examiner most often use to identify bullets and why?

barium, antimony

Determining whether an individual has fired a weapon is done by measuring the elements ____ and _____ present on the hands.

a. 18-20 in b. 6-8 in c. 1 in d. contact shot

From each of the following descriptions of bullet holes, use general guidelines to estimate the distance from the shooter to the target. a. A few widely scattered gunpowder particles with no soot around the entrance hole. b. A dark ring around the bullet hole, but no soot or gunpowder particles. c. A halo of soot surrounding the entrance hole along with scattered specks of powder grains. d. Scorch marks and melted fibers surrounding the entrance hole.

(A) 1 in (B) 6 in (C) contact (D) 18 in

Gunshot residue patterns (A) through (D) (contact, 1 inch, 6 inches, and 18 inches) from a 40-caliber pistol are shown in the figures. Match the firing distance to each pattern. (A) (B) (C) (D)

The wider the pattern the larger the distance. Barrel length, quality of powder charge, choke, size & quantity of pellets.

How is shot pattern used to make a distance determination for shotgun blasts? What factors other than distance to a target can affect the distance determination.

a. photograph the print; making cast b. photograph marked area to scale; make cast of the mark c. photograph tire marks; make cast d. photograph; bring tile to lab; use electrostatic lifting device e. photograph; use electrostatic lifting device or other adhesive-based lifting material

How would you go about collecting impressions in each of the following situations? a. You discover a shoe print in dry dirt. b. You discover a tool mark on a windowsill. c. You discover tire marks in soft earth. d. You discover a shoe print on a loose piece of tile. e. You discover a very faint shoe print in dust on a colored linoleum floor.

bullet wipe

If a firearm has been fired more than 3 feet from a target, usually no residue is deposited but a dark ring, known as _____, is observed.

1) altered by succeeding bullets or grit and rust in the barrel 2) evidence bullets are often damaged by distortion and mutilation

List 2 reasons why striations on bullets fired from the same gun may vary slightly.

lead vapor smoke rim, loose fibers, synthetic fiber melting, blowback ripping, star pattern (caused by gases)

List 3 characteristics of a bullet hole that indicate that the shot was fired at extremely close range.

caliber, number of lands and grooves, twist direction

List 3 characteristics of a gun barrel.

Scanning Electron Microscope (SEM)

Microscopic primer and gunpowder particles on the adhesives applied to a suspected shooter's hand can be found with a(n) ______.

1) damage from use 2) striations from manufacturing

Name 2 types of marks that impart individuality to a tool and explain how the marks are made.

photo or impression

Objects bearing tool marks should be submitted intact to the crime lab or a(n) _____ should be taken of the tool mark.

*Bullets should not be scribed*

Recovering bullets are initialed on either the ___ or ___ of the bullet.

photography, casting

Shoe and tire marks impressed into soft earth at a crime scene are best preserved by ____ and ______.

individual

The ____ characteristics of a rifled barrel are formed by striations impressed into the barrel's surface.

land

The ______ is the original part of the bore left after rifling grooves are formed.

National Integrated Ballistics Information Network (NIBIN)

The automated firearms search system developed by the FBI and ATF as a unified system incorporating both DRUGFIRE and IBIS technologies available in prior years is known as _____.

powder residues

The clothing of the victim of a shooting must be handled so as to prevent disruption of ____ around bullet holes.

gauge

The diameter of a shotgun barrel is expressed by the term ____.

caliber

The diameter of the gun barrel is known as the ____.

comparison microscope

The most important instrument for comparing bullets is _____.

striations

To make a match between a test bullet and a recovered bullet, the lands and grooves of the test and evidence bullet must have identical widths, and the longitudinal ___ on each must coincide.

striations

Tool marks compare only when a sufficient number of ____ match between the evidence and test markings.

true

True or false: A cartridge case can be individualized to a single weapon.

false

True or false: Because minute traces of evidence such as paint and fibers may be adhering to a recovered bullet, the investigator must take care to remove these trace materials immediately.

false

True or false: Cartridge cases are best marked at the base of the shell.

false

True or false: Firings with all types of ammunition can be detected by hand swabbings with nitric acid.

false

True or false: It is always possible to determine the make of a weapon by examining a bullet it fired.

false

True or false: It is proper to insert a pencil into the barrel when picking up a crime-scene gun.

true

True or false: One test method for locating powder residues involves transferring particles embedded on the target surface to chemically treated photographic paper.

true

True or false: Restoration of serial numbers is possible because in the stamped zone the metal is placed under a(n) permanent strain that extends beneath the original numbers.

false

True or false: Shotgun pellets can be individualized to a single weapon.

true

True or false: The distribution of gunpowder particles and other discharge residues around a bullet hole permits an approximate determination of the distance from which the gun was fired.

true

True or false: The number of lands and grooves is a class characteristic of a barrel.

false

True or false: Without the benefit of a weapon, an examiner can make an exact determination of firing distance.

record weapon's hammer, safety switch position and location of all fired and unfired bullets

What characteristics of a suspect firearm should an investigator record before unloading it? Why should the investigator number the chambers and cartridges when unloading a suspect weapon?

Presence of gun powder residue on the thumb web, back of hand and palm.

What evidence do investigators look for when trying to determine whether a suspect has fired a handgun? Where is such evidence typically found and why?

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. 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.

What evidence does an investigator study to make a distance determination? How can test-firing a suspect weapon help the investigator make a distance determination?

Process of determining distance from the firearm and the target, usually based on the distribution of powder patterns or the spread of a shot pattern. 1) area to look for evidence like shells, powder, trajectory of bullet 2) location of shooter

What is distance determination? Describe 2 situations in which distance determination can establish the facts of a shooting incident.

A chemical test that can detect gunpowder residues that are not visible 1) presence of a gunshot residue 2) distance.

What is the Greiss test and what 2 pieces of information can it provide to an investigator?

It must be photographed with scale included to show all observable details of impression. Photos should also be taken to show position of questioned impression in relation to overall crime scene. This is a backup just in case the impression is damaged before reaching the crime lab.

What is the first thing the investigator does before handling or moving an impression at a crime scene? Why is this considered merely a backup or precautionary procedure?

Safety and protection of class and individual markings

What is the investigator's primary concern when collecting and handling bullets and cartridge cases? Why must the investigator exercise extreme caution when removing a bullet lodged in a wall or other object?

An investigator should photograph the marked area to scale and make a cast of the mark. Under these circumstances, liquid silicone casting material has been found to be the most satisfactory for reproducing most of the fine details of the mark. However, the clarity of many of the tool mark's minute details will be lost or obscured in a photograph or cast. This will reduce the chance of individualizing the mark to a single tool.

What technique does an investigator use to analyze tool marks that cannot be removed from a crime scene? What is the disadvantage of this technique?

To produce markings similar to the evidence bullet.

Why does a firearms examiner test-fire bullets from a suspect barrel?

Due to hand washing, rubbing, wiping .22 caliber ammunition may contain only barium or neither nor antimony in its primer composition, which is different than other ammunitions

Why does analysis of primer residue from a suspect's hands produce a low rate of positive results? Why is such analysis typically ineffective in locating primer residue from a .22 caliber gun?se

Placing object in the barrel disturbs powder deposits, rust, dirt, blood that may have flown into barrel, affects striations in test fired bullets. Gun should be lifted by trigger guard or the checkered portion of hand grip.

Why would an investigator not pick up a weapon by its barrel with a pencil or stick in order to protect latent fingerprints? How should suspect firearms be handled in such a situation?

a. 18 yards because a spread pattern made by a 12-gauge shotgun increases by 1 in for each yard of distance and a moderately high choke would cause it to have just further than 12 yards distance.

You are investigating a shooting involving a 12-gauge shotgun with a moderately high choke. The spread of the pattern made by the pellets measures 12 inches. In your opinion, which of the following is probably closest to the distance from the target to the shooter? Explain your answer and correctly explain why the other answers are likely to be incorrect. a. 18 yards b. 12 yards c. 6 yards d. 30 yards