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forensics > forensics exam > Flashcards

forensics exam Flashcards

1
Q

Locard Exchange

A

when a criminal enters a crime scene a piece of them remains with the scene

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2
Q

direct vs circumstantial evidence

A

direct - first hand observations ex eye witness
circumstantial - indirect evidence that implies a crime is committed ex suspects gun

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3
Q

3 types of circumstantial evidence

A

physical - bullets, shoe/tire prints
biological - bodily fluids, hair
trace - small, measurable amounts of both: strand of hair, dan, fingerprints

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4
Q

class vs individual evidence

A

class - narrows evidence down to a group of people ex: blood type
individual - narrows evidence down to a person ex DNA

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5
Q

7 S’s of a crime scene

A

SECURE scene, SEPARATE witnesses, SCAN scene, SEE scene, SKETCH scene, SEARCH for evidence, SECURE + collect evidence

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6
Q

search patterns

A

spiral, grid, linear, quadrant/zone

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7
Q

DNA fingerprinting

A
  • distinguishes individuals based on DNA
  • developed by Alec Jefferys
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8
Q

DNA fingerprinting steps

A
  1. extract DNA
  2. Cut DNA into RFLPS (restriction fragment length polymorphisms)
  3. Amplification through PCR
  4. Gel electrophoresis - separates RFLPS according to length to create a DNA fingerprint
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9
Q

DNA

A

backbone is made up of deoxyribose sugar and phosphate molecules, double helix shape

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10
Q

complimentary nitrogenous base pairs

A

Adenine and Thymine
Guanine and Cytosine

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11
Q

exons vs introns

A

Exons = encoded DNA
Introns = non-encoded DNA, where variation is found

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12
Q

Polymorphisms

A

non-encoded DNA segments containing unique patterns of repeated base sequences

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13
Q

VNTRs and STRs

A

Variable numbers of tandem repeats (9-80)
Short tandem repeats (2-5)
these are applied through PCR and are analyzed for tissue or inheritance matching

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14
Q

Polymerase Chain Reaction (PCR)

A

make thousands of copies of DNA from trace evidence
steps:
- template DNA is mixed with nucleotides, DNA polymerase and Primers
- denaturations: temp increased to separate DNA strands
- Annealing: temp decreased to allow primers to base pair
- Extension: polymerase extends primers to form DNA strands

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15
Q

nucleotides and primers

A

Nucleotides: nitrogenous base, pentose sugar, phosphate
primers: short segments of complimentary DNA that base-pairs with template DNA

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16
Q

How Gel electrophoresis works

A
  • RFLPS are created
  • segments loaded into wells between cathodes
  • electric current is passed through gel
  • shorter smaller segments move faster towards positively charged cathode to create a DNA fingerprint
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17
Q

Genetic Genealogy

A
  • researches family history to create a family tree to match a DNA sample.
  • uses autosomal DNA (atDNA) and single nucleotide polymorphisms (SNPs) to determine how closely related 2 people are.
  • DNA data matches act as clues to build a family tree. they look for common ancestors across family trees to narrow down possible individuals who fit description
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18
Q

Fingerprinting

A

dactylography/dactyloscopy

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19
Q

components of fingerprints

A

made up of ridges ( appear darker) which help grip things and valleys (appear lighter)

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20
Q

when and how are fingerprints formed?

A
  • begin to form in 10th week of pregnancy
  • basal layer grows faster than layers above and below causing them to collapse and fold into intricate shapes
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21
Q

dots on fingerprints

A

fingerprints are porous - they have apocrine glands ( hair follicles) and eccrine glands (sweat glands) which secrete oils

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22
Q

minutiea

A

points where print ridges come together or end. they are unique

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23
Q

12 match guideline

A

analysts must find 12 matching minutiae

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24
Q

3 types of fingerprints

A

patent: visible prints left on smooth surfaces when blood, ink or other liquids touch surface
plastic: indentations left in soft materials ex clay
latent: not visible to naked eye caused by transfer of oils onto a surface

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25
Q

AFIS

A

automated fingerprint identification system developed by FBI as a fingerprint record database

26
Q

serology + blood typing

A

study of blood
blood typing - class evidence but DNA profiling from blood is individual evidence

27
Q

components of blood

A

Erythocytes (RBC) - contain hemoglobin which carries oxygen and makes blood red
Leukocytes (WBC)
Platelets (Thrombocytes)
plasma

28
Q

blood types

A

determined by angulation (clumping). A and B proteins found of surface of blood cell

29
Q

universal donor

A

O

30
Q

Blood spatter

A

grouping of blood stains that can help reconstruct a crime and help solve it

31
Q

blood spatter determines

A
  1. direction blood travelled in
  2. angle of impact
  3. point of origin
  4. velocity of blood
  5. manner of death
32
Q

how does blood fall/spatter

A

cohesion: blood sticks together to form a round shape.
satelitte droplets can form (small secondary droplets
spikes can also form (extensions around edges
elongated drops determine it fell from a different direction and lines of convergence can be used to determine blood source

33
Q

different kinds of blood spatter

A
  • passive drops: 90º cohesion drops with satellites and spikes
  • arterial gushes
  • splashes: depict victims position
  • smears: blood smeared by touching things. swipe: transfer of blood to another surface, wipe: object moves through blood that isn’t dried
  • blood trails: show victims movements
    -blood pools: victim bleeds heavily
  • cast off: blood flying off the surface of a blood object. cessation cast off= pattern was interrupted
34
Q

Presumptive tests

A

establish the possibility that a specific body fluid is present
ex: Luminol: detect hemoglobin left behind after blood was cleaned. turns blood luminiesce for 30 seconds then destroys it
Kastle-Meyer test: swab turns pink if blood is detected

35
Q

confirmatory tests

A

identify a specific biological material
ex: elisa (enzyme-linked immunisisorbent assay) uses antibodies that react to human blood to determine is mammal blood is human.

36
Q

crime scene investigation of blood steps

A
  1. confirm stain is blood (presumptive tests)
  2. confirm stain is human (confirmatory test)
  3. determine blood type
  4. DNA analysis
37
Q

death

A

irreversible stopping of blood circulation and brain activity

38
Q

autolysis/self-digestion

A

lysosomes breakdown and release digestive enzymes. when heart stops beating, oxygen stops circulating and cells die

39
Q

autopsies determine…

A

manner, cause, mechanism, and time of death

40
Q

5 manners of death

A

natural: natural failure of body functions due to age or disease
accidental: unplanned event ex car accident or fall
suicidal
homicidal
undetermined

41
Q

livor mortis

A

death colour - pooling of blood after death - lividity
blood settles in lower body as RBCs break + release hemoglobin.
begins 2-8 hours after death and after 8 hours discolouration is permanent
this can help determine the position of the person when they died and if they were moved

42
Q

rigor mortis

A

death stiffness - skeletal muscles stiffen
after death. stiffness begins 2 hours after death, is stiffest after 12 hours but it goes away after 36 hours as the cells dissolve. this process is slowed by cooler temperatures

43
Q

algor mortis

A

death heat - cooling of body after death and body loss of temperature because body no longer maintains hemostasis.
body temp is monitored by a thermometer in the liver

44
Q

5 stages of decomposition

A
  1. fresh (0-2 days): instantly after death, all mortis occur. as autolysis sets in, blisters form
  2. bloat/ putrefaction (4 days): due to activities of microorganisms. characterized by the production of gases which causes bloating and strong odours. skin turns green and fluids flow from openings in the skin
  3. active decay (6-10 days): great loss in mass due to maggots and other insects eating flesh. body turns black and may collapse as it leaks fluids. this stage is over when maggots leave
  4. advanced decay (10-20 days): adipocere: wax layer formed by the body
  5. dry remains: all that is left is dried up bones
45
Q

ballistics

A

scientific analysis of firearms, bullets, travel of projectiles in flight.
began when Chinese invented gun powder used for fireworks

46
Q

muzzle-loader guns

A

shooter manually packs gunpowder and bullets down the barrel
matchlock: used wicks to ignite
flintlock: used sparks from flints to ignite gun powder

47
Q

breech loaders

A

replaced muzzle-loading firearms with cartridges

48
Q

cartridges

A

aka rounds = case holding a bullet (small amount of exploding primer) and gunpowder
primer= a volatile compound that ignites when struck by firing pin of gun
gunpowder is the propellent that forms gases to push bullet from cartridge and the bullet casing is left behind

49
Q

modern firearms

A

handguns and long guns

50
Q

handguns

A

fired with 1 hand = pistols
pistols with several cartridges = revolvers because the can be continuously fired and have a 12lbs trigger pull

51
Q

semiautomatic and revolver handguns

A

revolvers = 6 cartridges
semi automatics = 10 cartridges in a magazine clip, fire 1 bullet per trigger pull and automatics continuously fire as long as trigger is pulled

52
Q

glock

A

debuted in 1980s
hold 17 rounds with 5 lbs trigger pull

53
Q

long guns

A

rifles and shotguns requiring 2 hands to shoot
rifles: fire bullets. automatics are strictly meant for killing people because they are too much for regular hunting
shotguns: fire shots (small round projectiles) or slugs (solid piece of metal). shells are different from rounds because of the wad - a plastic piece separating shot from powder

54
Q

3 basic compositions of bullets

A
  1. lead: cheap, dense, soft+easy to mold
  2. 1/2 jacketed: lead Buller half covered in copper to improve velocity. lead promotes mushrooming
  3. jacketed/full metal jacket: copper improves exit velocity and holds the bullets shape for max penetration
55
Q

caliber

A

how bullets are named
the diameter of a bullet measured in mm and matched the diameter of the inside of the barrel of the firearm

56
Q

GSR

A

-Gun Shot residue
residue left from the gun after it has been fired and the gunpowder has exploded
its trace evidence from smokethat can land on the perp or the victim
it can determine the distance between the shooter and the victim

57
Q

how GSR is collected

A

since its so fragile it must be collected quickly. hand protection bags are wrapped around shooters hand (after they committed suicide) to on the hands of the victim to preserve the GSR

58
Q

Modified Griess test

A
  • a piece of desensitized photographic paper is traced with a chemical mixture of sulfanilic acid in distilled water and azpha-napthol in methanol. this makes the paper reactive to the presence of nitrite residues
    -evidence is placed on the paper and then steam ironed with dilute acetic acid solution
    -these acidic vapours will penetrate the evidence and a reaction happens between any nitrite residues on the evidence and the chemicals on the paper
    this results in orange speck on the paper
59
Q

entrance bullet wounds

A

-smaller because the skin must stretch as bullet enters
- clothing fibres might be embedded in the wound and GSR may be found in and around the wound
- burn marks may be evident is its a close range shot
- abrasion rings: from when the force of the gases entering blow the skin surface back against the muzzle of the gun
- grey/black discolouration from the soot and abrasion ring

60
Q

exit wounds

A

-larger because bullet carries tissue and bone that it picks up as it moved though the body
- fast-moving high caliber bullets tend to pas through the victim, small caliber low velocity bullets stay lodged in body
-no powder or soot is visible

forensics (2 decks)

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