Forensic Science Unit 10 Notes
What is the condition that facilitates a flash point?
Vaporization of a liquid due to weak molecular bonds.
What are the net products of the chemical combustion reaction of glucose polymers such as cellulose?
Water, CO2, Heat
You are a fingerprint expert, and an arson investigator asks you if you can come down to a newly burned building and look for fingerprints. What would be an acceptable response?
"Sure, let me get my kit because intense heat causes fingerprints to stick to many surfaces."
Cartridges are stored in a cylinder.
Revolver
Has a rifled barrel and cylinder but is not semi-automatic
Revolver
Arson is typically suspected when the fire pattern is _____.
Ribbon shape
Shoulder firearm that fires bullets.
Rifle
Why don't shotguns have rifled barrels like pistols and rifles do?
Rifling helps a bullet spiral so that it travels in a straight line improving accuracy. Shotguns do not need rifling because they fire shot pellets which are designed to have a wider spread.
What causes cavitation?
Shock waves
Barrel is not rifled
Shotgun
Cartridges contain pellets called shot.
Shotgun
What are the marks on the bullet above called?
Striations
Primer
1
Lift the handgun by this part which likely has no fingerprints.
10
Press this button to eject the magazine.
12
Flash hole
2
Cartrige
3
To ensure the pistol is safe, flip this switch so the red dot is hidden.
3
Metal jacket
4
Bullet
5
Gunpowder
6
When the slide is racked, any chambered cartridges will pop out from this area.
6
Pull this part backward to check for chambered cartridges.
7
Rim
7
Lands and grooves that produce striations can be found here.
9
Victims A and B survive gunshot wounds to the abdomen. Victim A displays a half-inch area of reddened skin around the entrance wound. Victim B displays a one-inch area of reddened skin around the entrance wound. Which victim was likely shot from a closer distance?
A
Generally speaking, why do caliber measurements of barrel bores and cartridges have to be the same? In your explanation, state what a caliber measurement tells about the bore and the cartridge.
The caliber of a cartridge is the diameter at the widest part of the width of the cartridge, and it would make sense that it matches the bore diameter as the cartridge must fit snugly within the barrel.
What is the common name of the pattern in the images? Describe what you can determine from patterns A and B. Which one shows wood that burned hotter, and how can you tell?
The common name for this pattern is alligator skin. The image on the right with the smaller scales indicates that it burned hotter.
Name three pieces of evidence that would allow you to distinguish an entrance wound from an exit wound in human skin.
stippling, muzzle burn, carbon monoxide burn, and abrasion ring, etc.
With a bomb signature, you might be able to determine _____.
the maker of the bomb based on the choice of materials used
You arrive at the scene of an extinguished building fire and notice that there are multiple points of origin. What do you suspect?
An accelerant was likely used
You are investigating a crime scene and a junior investigator discovers a firearm. He uses his pen to insert into the barrel to lift the firearm so that he doesn't get fingerprints on the weapon. What do you say to your coworker?
Don't do that again. Lift by the trigger guard.
Which of the following are high explosives? Select all that apply.
Dynamite, TNT, C4
What is responsible for the heat and light you see in a fire?
Energy emitted from breaking and reforming molecular bonds
Explain how you would contain the evidence items you collected in an arson case, and why you would choose such a container. Then explain how you would prepare the container to test for accelerant vapors.
Evidence is stored in new metal paint cans because they are airtight and will not allow any possible accelerant vapors to escape. Once in the lab, the cans are heated to vaporize any possible accelerant so the vapor samples can be tested.
Exit wounds are always smaller than entrance wounds.
False
Spontaneous human combustion (SHC) is a real phenomenon.
False
What are the conditions that contribute to spontaneous combustion? Select all that apply.
Material with a low auto-ignition temperature Bacteria that cause fermentation
Which of the following is an incendiary device?
Molotov cocktail
Cartridges are stored in a magazine.
Pistol
Semi-automatic weapon with a rifled barrel
Pistol
Why is lead styphnate used in the primer space rather than plain gunpowder? What is the difference?
Primer material such as lead styphnate is explosive and can be ignited with frictional impact. Gunpowder is more stable and must be ignited with a flash or flame.
Where would you likely see severe tearing of skin when discovering a gunshot victim? What causes the tearing?
A contact gunshot to the head causes pressure from the explosive gases to expand and separate the skin from the bone causing tearing of the skin. Tearing of skin is also common in intraoral gunshot wounds due to the explosive gases that tear facial skin around the mouth.
The technical term for an explosion whose outward expansion is subsonic is called ______.
A deflagration
Which most closely aligns with the definition of an improvised explosive device?
A pipe bomb
One of the following statements is true. Three are not. Choose the true statement.
At auto-ignition temperature a material can ignite all by itself.
You are investigating a suspected arson case. Where do you begin your investigation?
At the areas that are the least burned
What type of cartridge is pictured above?
Centerfire
A handgun and a shell casing, or spent cartridge, is found at a crime scene, but no bullet is recovered. Firearms analysts test fire the same type of ammunition and discover that the firing pin impressions look identical. What type of evidence is this?
Class evidence—Firing pin impressions are not individual enough to link a cartridge with a gun.
How can an arson investigator determine whether glass at an arson scene was broken before or after the fire?
Curved lines on the edges of glass means glass shattered because of an impact. Smooth edges mean the heat of a fire caused the glass to break.
Illegal without a special permit
Fully automatic weapon
You receive evidence in the lab that might contain volatile vapors. Your job is to separate and identify vapor molecules in possible accelerant evidence obtained from a house fire. Which instrument will serve you best?
GCMS
A house is set on fire, and the firefighters are doing their best to extinguish the blaze. As an investigator, where is a likely place the arsonist can be found?
In the crowd or nearby watching the destruction.
If the bullet is linked to the gun by comparison of striations, what type of evidence is this?
Individual evidence—the bullet came from that specific weapon only.
If the burn marks of a fire suggest a V shape, what can one conclude about the fire?
The fire started at the bottom of the V
Arson experts know that three things are required for a fire to begin: fuel, oxygen, and heat. These three things are collectively called _____.
The fire triangle
If steel beams have buckled in a building that is on fire, it suggests that _____.
The fire was likely started using an accelerant
The image above shows an entrance and exit wound in a human skull plate. Which is which, and how can you tell?
The first one is the exit wound as evidenced by the beveled edges in the bone. In this case, it is the larger diameter wound, but that is not always the case in tissue.
You're called to a crime scene where a man has been killed with a bullet to the side of the head. The man's wife says that he was distraught and before she could scream, he put the gun to his head and fired. You decide to check for gunshot residue on both the victim and his wife. Where would you collect GSR evidence first in order to verify or refute the wife's story?
The skin between the thumb and index finger of both victim and wife.
Oftentimes, criminals file off serial numbers on a weapon. What is the accepted protocol for restoring serial numbers that have been obliterated?
They can use an acid wash or magnetic particles.
If one handgun and only one bullet are found at a crime scene involving a homicide, how will firearms investigators test the striation patterns on that bullet?
They will test fire a bullet through the gun and match the striations on that bullet with the striations on the evidence bullet.
Which type of gunshot wound will likely not produce stippling?
Tight contact wound
Why do people commit arson?
To cover up a murder or other crime. To exact revenge on a person or company. To terrorize a person or people. To collect insurance money.
