Physical Evidence

Physical Evidence Prints and impressions (tires, shoes, fingers)

Footprint at scene saidto Match Avila’s OC Register, 4/5,05 • Samantha was kidnapped in July 2002 whileplaying in front of her home with a friend. Herbody was found the next day. She had beensexually assaulted, then suffocated. • Sgt. Robert Kennedy, an RCMP expert onfootprint comparison, testified that afootprint found near the body haddistinct characteristics that matched Avila’s right foot. • Mark Johnson, an Orange County Sheriff’s crime lab forensic specialist, testified that shoeprints found near the body had a pattern matching a size 12 Fila Disrupter tennis shoe. • Mark Johnson also testified that tire prints found at the scene were of the same size and design as the Michelin tires on Avila’s 1994 Ford T-Bird.

Prints • Prints are made when an object deposits a two-dimensional pattern • Patterns are deposited by raised sections, or “ridges” • Deposits can be visible or latent • Latent prints become visible through development • Visible or developed prints are photographed and (if possible) lifted • Given sufficient “points of ID” prints can be individually matched to a person or object

Impressions • Impressions are made when pressure from an object creates a three-dimensional image on a soft surface • Impressions should FIRST be photographed; then, if possible, cast • Given sufficient “points of identification”, impressions can be individually matched to a person or object • Unusual impression: pattern of pedestrian’s clothing on vehicle paint

Shoes • Class characteristics • Identify brand and model from outsole designfeatures • Computer-assisted matching • Individual characteristics • “Points” of comparison, from questioned to known

Tires • Class characteristics • Can identify tire brand and model • Can identify vehicle brand and model using that tire • Can identify vehicle brand and model • Having the measured track (width) and wheelbase (length) • Individual characteristics • May identify specific tire from wear and damage (“points of identification”)

Fingerprints • What are they? • Outlines of ridges where sweat glands are present • How are they deposited? • Inked • Stained or dirty hands • Impressions on soft materials (“plastic prints”) • Body secretions (sweat and other chemicals)

Developing fingerprints • Making visible (“developing”) • Special light sources (u.v., laser) • Dusting with materials that adhere to body secretions • Light & fluorescent powder • Chemicals to darken body secretions • Ninhydrin • Superglue fuming  • Photograph before lifting • Special conditions • Fingerprints on paper • Fingerprints on bodies • Fingerprints on greasy surfaces

Identification • Common patterns • Loop • Whorl • Arch • Common minutiae • Islands • Dots • Bifurcation • Ridge endings

Comparison • Compare pattern (loop, arch, whorl) • If similar, then compare minutiae (where ridges start, stop and separate) • Islands, dots, bifurcations, ridge endings • Set number of points (6-15) must be identical in type and location with known print to make an identification • “Locations” found as on a map and by counting ridges

AFIS • Old system required having a suspect in mind, with a 10-print card on file • Questioned print compared to card • New system – AFIS • Digitizes 10-print cards from arrested persons • Digitizes prints recovered at crime scenes • Compares both, looking for possible matches • Makes suggestions • Final match must be done in the conventional way, by comparing minutiae

Physical Evidence