Dactyloscopy

…the study of

fingerprints

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 RidgesCan 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 SystemLooking 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 Little

AddedAutomatically

FINALGROUP

  +   +   +   +   + 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

Visible; from a finger that has touched colored material such as blood, ink, paint, mud, dust, etc.

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 VIDEODeveloping prints with superglue video

CHEMICAL METHODS