Lecture 10: Physical Evidence IV (Fingerprints) Flashcards
What are the three layers of skin in vertebrate animals?
Epidermis, Dermis, Hypodermis
The hypodermis is often not mentioned in basic discussions of skin layers.
What are the two assumptions regarding fingerprints for personal identification?
- The fingerprints of an individual stay unchanged throughout life
- No two fingerprints are identical.
Why do we have fingerprints?
- More friction -> better grip
- Prevent skin from tearing early
- Improve sense of touch
What are the three main classifications of fingerprints?
- Arch
- Loop (most common 65%)
- Whorl
What is a core?
Center of a loop or whorl
What is a delta?
A triangle ridge pattern
What type of fingerprint pattern has no deltas?
Arches.
What is a characteristic feature of tented arches in fingerprints?
They have a spike in the center.
Describe the features of loops
- One delta
- One or more ridge that leave on the same side
- Named according to position relating to radius and ulna
Describe the features of whorl
- Two or more delta
- One or more ridge (forms complete circuit)
What are the four subtypes of whorls in fingerprint classification?
- Plain whorl
- Central pocket whorl
- Double loop whorl
- Accidental whorl.
How to differentiate between plain whorl and central pocket whorl?
What is the primary characteristic of double loop whorls?
Made up of any two loops combined into one print.
What are the three main categories of fingerprints?
- Visible/patent
- Plastic
- Latent
What are visible fingerprints?
- Visible by naked eye
- when an appropriate substance is transferred by the fingertips onto a suitable surface
- e.g. inks, blood
What are plastic fingerprints?
Fingerprints pressed into a suitably soft material such as putty or clay.
How are latent fingerprints different from visible and plastic fingerprints?
Cannot be seen with the naked eye
What is the composition of latent fingerprints?
Perspiration exuded from sweat pores, containing 95% water and 5% other substances including salts and amino acids/ body oil and grease
Name the 7 methods for development of latent fingerprints
• Fluorescence examination
• Superglue fuming
• Iodine fuming
• Powders
• Acid dyes
• Ninhydrin and/or DFO application
• Gentian violet
What technique is used for developing latent fingerprints on non-porous surfaces (e.g. rubber/metal)?
- Superglue fuming (ethyl cyanoacrylate)
- Apply before applying powders/dye stains
- Cyanoacrylate vapors adhere to amino acids left behind by fingerprint secretions
What substance is used for porous surfaces (e.g. paper) for latent fingerprint development?
- Ninhydrin
- Reacts with amino acid to give bluish-purple color
- spray with ZnCl2 for fluorescence
What is the oldest technique to develop latent fingerprints?
- Ioding fuming
- On any surface
- Heat iodine solid and undergo sublimation
- fingerprint reacts with iodine vapor to form yellow-brown print
What is a common visualization technique for fingerprints on hard surfaces?
- Powders
- Adheres to grease or dirt
- For hard, relatively smooth, non-porous surfaces
How do acid dyes develop latent fingerprints?
- For fingerprints contaminated with blood
- Stains proteins present in blood e.g. RBC
- e.g. acid black 1, acid violet 17, acid yellow 7
