1
Q
How Is Impression Evidence Classified?
A
- patent
- latent
- plastic
2
Q
Patent
A
- visible to the naked eye and doesn’t require special enhancements or development techniques
- objects covered in blood, ink, etc touches a surface and transfers characteristics of the object
- 2D
- eg. bloody fingerprint
3
Q
Latent
A
- hidden to the naked eye, must be made visible with forensic enhancements
- 2D
- oils, sweat, other substances from the skin transferred to a surface = faint/hidden mark
- eg. sweaty footprint on glass
4
Q
Plastic
A
- visible to the naked eye w/out enhancements
- 3D
- objects contact a soft surface like wax, mud, clay, snow, etc
- eg. fingerprint in wax
5
Q
How do fingerprints form?
A
- the main pattern is made from our genes
- volar pads develop around the 6-8th week of embryonic development. Stops growing at 10 weeks while hands continue to grow
6
Q
Basic Ridge Patterns
A
Whorls, loops, arches
7
Q
Arches
A
- plain arch (loops enter one side, rise center, and exit the other side)
- tented arch (spike in the center)
8
Q
Loops
A
- radial loop (points to the thumb)
- ulnar loop (points to the pinky)
9
Q
Whorls
A
- double loop whorls (two loops and two deltas)
- accidental whorl (doesn’t align w/ any category)
- plain whorl (curved ridges touch line)
- central pocket whorl (curved ridges don’t touch the line)
10
Q
Types of Minutiae
A
- forks
- double forks
- triple forks
- deltas
- dot
- bridges
- hook
- eye
- short ridge
- ending ridge
11
Q
How are LATENT fingerprints processed?
A
- physical
- chemical
- alternate light source
12
Q
Physical
A
Dusting powders: fine particles stick to the fingerprint residue and make it visible. It’s then lifted w/ transparent lifting tape and put onto an evidence card.
- magnetic powders can also be used
13
Q
Chemical
A
Iodine fumigation or cyanoacrylate (superglue): enclosed cabinet with object and vaporized versions of these two; allowing the amino acids, proteins, and fatty acids within the print to react w/ the superglue = white colour. The iodine combines w/ the carbs in the latent print = brown colour.
14
Q
Alternate Light Source
A
- latent prints may be revealed under alternate light or laser illumination
15
Q
What do footprint impressions reveal about a crime scene?
A
- wear pattern
- height
- weight
- person’s gait
- footprint profession
- pigeon toed, duck feet, or normal walking
- how they’re moving (running, walking)
16
Q
Estimating height using foot length
A
Use formula, remember to subtract 1.5 from the length of the foot, and that there’s a 5cm difference
17
Q
Estimating height using stride length
A
Use formula, remember there’s a 5cm difference
18
Q
How is footprint impression evidence collected?
A
- Photographing
- lifting
- electrostatic dusting
- gel lifting
- casting
19
Q
Photographing
A
- especially important as they prove the evidence was indeed at the crime scene
- MUST: take pics as is with and without a ruler so it’s not altered, perpendicular, multiple pics, and indirect lighting so there’s now glare
20
Q
Lifting
A
- used for latent footprints hidden to the eye
- uses: luminol for blood, dusting, electrostatic lifting, and gel lifting for uneven surfaces
21
Q
Electrostatic Dusting
A
- best used for fine dust left behind by a dry shoe, latent, flat surface that is dry
22
Q
Gel Lifting
A
- best used for latent prints, oily, or moist impressions. The gel is not sticky so you could even lift off of paper
23
Q
Casting
A
- for sand and soil, hairspray may be used to keep the impression intact and preventing it from collapsing under the weight of the plaster
- for impressions in snow, snow print wax will be used as it hardens, doesn’t melt the snow, and provides protection for the delicate impression
24
Q
What is forensic odontology?
A
- a field that combines the skills of a specially trained dentist w/ those of law enforcement
- study of teeth with the intention of providing facts to be used as evidence in court.
25
Parts of Teeth
Incisors
Canines/Cuspids
Molars (Premolars/Molars
26
Incisors
- 2 central incisors
- 2 lateral incisors
= 8 total
27
Canines/Cuspids
- 4 canines
- 2 on the bottom, 2 on top
28
Molars (Premolars/Molars)
- 8 premolars/bicuspids
- 12 molars (1st, 2nd, 3rd)
= 20 total
32 teeth in an adult
29
Tooth Structure
Enamel, dentin, and pulp
30
Enamel
- protects teeth from damage while eating, resistant to decomposition, and hardest tissue in the human body
31
Dentin
- helps support the structure of the enamel, helps absorb pressure from eating
32
Pulp
- creates dentin + provides tooth nutrients, its DNA can be used for DNA analysis + identification
33
Crown, root, and neck
Crown: visible part of tooth, above the gum line
Root: hidden part of the tooth within the gum line
Neck: when crown and root meat/gum line
34
How do you know if it's a bite mark?
- 2 u-shaped arches separated by a space @ their base
- series of round bruises + possible small marks
- front teeth are primarily shown (6 upper and 6 lower present on the bite)
35
How are bite marks analyzed?
1. Determine which marks are upper and lower
2. Determine which marks were made by which teeth
3. Measure the bite mark
4. Compare the suspect and the bite mark to each other
36
Is bite mark impression evidence valid?
- bite marks are rarely definitive (as in not the MOST important like a fingerprint)
- they should be used to EXCLUDE not INCLUDE suspects
- they're more so opinion based
- 63% rate of false identification
37
Case Study
Ted Bundy:
the 5 factors left behind by the physical evidence are:
- shape of bite
- sharpness of various teeth
- rotation of individual teeth
- location of chips
- and size of each tooth
Sharon Zachary
- tennis shoe print on the glass she stepped on. The nicks and scrapes matched the shoe she had at home
- fingerprint on the belt matched her left thumb
Jose Castillon
- the tire impression left behind in the mud revealed it was sold in Colorado, could see the brand name, and that they were snow tires. Uncommon in a state where there was barely any snow
- there was a bloody fingerprint on the victims left thigh. It was enhanced with amido black. And the FBI were able to separate the print of the finger from the pattern of the skin, revealing it to be Elias’s middle finger on his right hand
38
Determine which marks are lower + upper
- upper is wider
- upper has two incisors
39
Determine which marks were made by which teeth
- incisors r rectangular
- top central incisors r wider than lateral incisors
- 4 smaller rectangles = incisors
- cuspids leave dots
- premolars and molars = leave dice shaped marks
-blank spots = missing teeth, gaps, damaged tooth, smth in the way, etc
40
Measure the bite mark
- tooth mark size
- distance between teeth
41
Compare the bite mark to the suspect(s)
- transparent overlays or photos may be used for comparison
- wax impressions can be obtained from the suspect(s)
42
Fingerprint Classification
- loops are 60-65%
- arches are 5%
- whorls are 25-30%
Forensics - Impression Evidence
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