How firearms are collected.
The gun will be unloaded, a note made about the position of the gun's safety and hammer, each round taken from the firearm is placed in a separate envelope, chain of custody is noted, marked for identification purposes, identification tag attached to trig
Part of gun least likely to contain fingerprints.
Trigger guard or checkered portion of the grip.
Done if a gun is found in water.
Gun should be transported to the laboratory in enough of the same water to keep the gun submerged. It should not be dried or cleaned before it is transported, as this can cause the gun to rust.
Happens if bullets aren't handled carefully.
Striation marks might be damaged.
Done when the bullet is retrieved.
Usually marked with the investigator's initials, often at the tip or base of the bullet. Can be placed into a marked container for identification purposes.
Reason the sides of the bullet should not be marked.
Can not cover or obscure any striations or markings on the bullet.
How bullets are transported to the lab.
Wrapped in tissue paper and placed in an envelope or pillbox. Paint or fibers might be present that could be important to the investigation.
Done when clothing is collected analysis.
Should be removed as carefully as possible to avoid tearing or disrupting any possible gunpowder residue. Each item should be placed in its own paper bag. Any wet item should be air dried out of the sun and then placed in a paper bag.
Firearm identification
Includes the identification of bullets, knowledge of weapons, the detection of gunpowder on garments and hands, and estimations of bullet trajectory and distance.
Bore
The gun barrel.
Rifling
Spiral grooves cut into the barrel of a gun in order to make a bullet spin as it is fired. Produces grooves or lands.
Grooves
Low areas cut into the barrel
Lands
Raised areas between the grooves.
Caliber
Diameter of the gun barrel. Typically measured in millimeters or one hundredths of an inch.
The Integrated Ballistic Identification System (IBIS)
A database of digital images showing the identifying features of bullets and casings.
National Integrated Ballistic Identification Network (NIBIN)
This network provides law enforcement agencies around the world with access to the images and information. The network has provided law enforcement officials with thousands of matches in the decade that it has been in use.
Magnitude
Another word for size.
Scalar Quantities
Quantities that can be described completely by their magnitude.
Vector Quantities
Quantities that require both a magnitude and direction for a complete description.
Doppler Effect
At a racetrack, sound is different before it reaches you compared to after it has passed. The sound is much higher pitched before and lower pitched after it passes. This is because sound waves get stretched behind a traveling object.
Distance Determination
The process of estimating the distance between where a shot is fired and its target.This is often done by looking at the patterns of powder residue and the shot pattern.
Factor that influences the accuracy of a distance determination.
Whether the firearm in the shooting has been recovered or not.
What happens when a gunshot is part of a crime scene.
Forensic scientists will examine clothing and other objects from the scene for gunpowder residue.Chemical tests may also be used to show any residue. The Greiss Test uses chemicals to develop gunpowder residue patterns, particularly around bullet holes.
Tools used for measurements.
Rulers, balances, thermometers, and graduated cylinders.
Where residue is most likely to be on the shooter.
Most likely to show up on the thumb web (the area between the thumb and fingers) and on the back of the hand, but the residue can be distributed to other areas of the hands and arms as the gun is handled or other activities are performed.
Tool Mark
When a tool comes into contact with another surface and creates a scratch or impression.
Done when tool marks are found.
Photographs are one of the first steps. Close-up photographs with the right light can show individual characteristics. Then the object is taken to the lab. A cast of the impression using silicone rubber or filled plastics is often made of the impression.
Why it's difficult to find the weapon that caused the tool mark.
Investigators may have to use different amounts of pressure and use the tool from different angles.
Serial number.
A number impressed somewhere on the good for identification purposes.
How serial numbers are removed.
By grinding or punching the area where the serial number is.
How to get serial numbers on an item.
Manufacturers typically strike stamps a piece of metal on the item with steel dies. The dies hit the metal and form an impression of the serial numbers