fingerprints are useful because… they’re unique they’re consistent over a person’s lifetime...
TRANSCRIPT
Fingerprints are useful because…• they’re unique• they’re consistent over a person’s lifetime• we have a systematic classification scheme
Why do we even have these ridge patterns?• provide a better grip? (friction ridges)• make perspiration easier on a hairless surface?• improve our sense of touch?
Apes and monkeys also have them on fingers and toes
Friction Ridges
Can also be found on your palms, feet, and lips
They are NOT genetically controlled…even identical twins have different fingerprints!
Sweat pores along ridges release perspiration made up of 99% water. After evaporation, the remaining residue consists of salts, organic compounds, and body oils.
3 Basic Patterns:
1. Loop; at least one ridge enters and leaves from the same side
a. Radial loop opens to radius bone (thumb side)
b. Ulnar loop opens to ulna bone (pinky side)
Contain a core and a delta
3 Basic Patterns:
2. Whorl; at least two deltas and a core
4 types: a. Plain whorl b. Central pocket c. Double d. Accidental
3 Basic Patterns:3. Arch; ridges enter on one side and exit on the other(usually no delta or core)
Types; a. Plain b. Tented
Frequency:
60%
20%
10%
5%
4%
1%
Plain arch
Other whorls
Ulnar loop
Tented arch
Radial loop
Plain whorl
Ulnar loop
Plain whorl
Other whorls
Radial loop
Plain arch
Tented arch
Henry Classification System
Looking for whorls!!!Pg. 81
R. Index R. Ring L. Thumb L. Middle L. Little
------ ------ ------ ------ ------
R. Thumb R. Middle R. Little L. Index L. Ring
16 8 4 2 1
Right Index
Right Ring
Left
Thumb
Left Middle
Left
LittleAdded
AutomaticallyFINALGROUP
+ + + + + 1
------ ------ ------ ------ ------ ------ = ------
+ + + + + 1
Right Thum
b
Right Middl
e
Right Little
Left Index
Left Ring
AddedAutomatically
FINALGROUP
Ridge ClassificationINDIVIDUALIZING PRINTS
Individual ridge characteristics are called minutiae.
No legal requirements in the US regarding the number of points that must match before deciding that a fingerprint belongs to a certain individual.
Criminal courts generally accept 8-12 points of similarity.
Types of Fingerprints
Plastic; indented or molded prints made by pressing a finger into a plastic-like material
Latent prints; made by the deposit of perspiration or body oils. These prints are invisible to the naked eye until “developed” by some chemical or physical means.
Visualizing Latent Prints“Dusting” for prints; • Use fine powder that adheres to body oils and
perspiration• Use a powder that contrasts with the surface (ex. Use
white powder on a dark surface and black powder on a light surface)
• Brush away excess powder that does not adhere to the print
• “Lift” the print with clear, sticky tape• Works best on hard, non-absorbent surfaces
DUSTING FOR PRINTS VIDEO
Developing prints with superglue video
CHEMICAL METHODS