Forensics - fingerprints

plain arch

• no deltas

tented arch

• delta is present, what makes it tented

radial loop

• one core

• one delta

• bottom of loop points towards the thumb

ulnar loop

• one core

• one delta

• bottom of loop point towards the pinky

central pocket whorl

• 2 deltas

plain whorl

• 2 deltas

accidental whorl

• 2 or more deltas

• combines 2 or more other patterns, but not a tented arch

double loop whorl

• 2 loops

• 2 cores

• 2 deltas

bifurcation

• looks like a fork

island

enclosure

eye

spur

• hook

trifurcation

delta

double bifurcation

dusting

• fine dust (often charcoal) stick to the sweat and oils on prints

• works best on smooth surfaces

• excess dust blown away, then photographed

• lifted with tape then placed on collection card

• can be messy, too faint

iodine fuming

• get print from porous surface ( paper, cardboard, wood)

• solid iodine is heated in vapor tend and produces vapor (sublimation)

• Iodine crystalizes on prints, form brown color

• fades unless sprayed with starch solution

• not common, toxic and not sensitive

ninhydrin

• best for prints off of paper

• sprayed with solution of ninhydrin in acetone or alcohol

• reacts with amino acids in sweat and becomes purple-blue

• takes up to 24 hours to form, toxic and flammable 

cyanoacrylate fuming

• prints on plastic, metal, or glass

• items put in “vapor tent” and exposed latent fingerprints to cyanoacrylate by heating superglue

• reacts with amino acids and water and becomes a white solid (harder to see)

• good for preserving the print

How/when do fingerprints form?

• form on the fetus in the womb

• the basal layer of the skin grows faster than the epidermis and the dermis, which makes it wrinkle into patterns

• twins don’t have the same prints and they are not genetic

 

epidermis

Outermost layer, protection against environmental hazards, pathogens, and water loss.

• produces melanin for skin pigmentation

dermis

Middle layer, blood vessels, nerves, and connective tissue. Provides structural support and has hair and sweat follicles.

• temp regulation and sensation

hypodermis(subcutaneous layer)

Innermost layer, has fat and connective tissues. Acts as an insulator, absorbs shock, and anchors the skin to inner structures.

Basal layer

Between Epidermis and Dermis, important for skin regeneration, pigmentation, and treating wounds.