Physical Evidence

Prints and impressions

(tires, shoes, fingers)

\Wrongful arrest,conviction\FBI Portland case.wmv\DNA and phys evid\church fires tire.wmv

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– Identify tire brand and model– Identify vehicle brand and model– Identify vehicle brand and model from

track (width) and wheelbase (length)

Individual characteristics– May identify specific tire from wear and

damage (“points of identification”)

Church fires (March 2006)– Agents found tracks from a BF Goodrich

all-terrain tire– Witnesses to several fires described a

Toyota SUV– Agents checked tire dealers for

purchases, came up with suspect’s mother

– Father said son confessed to him

Advanced Imaging and Analysis.com

Impression in mud compared to suspect’s tire

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

Island Dot Bifurcation Ridge ending

Common minutiae– Islands– Dots– Bifurcation– Ridge endings

policensw.com

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

policensw.com

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

Fingerprint comparison not foolproof

Subjectivity Sloppy work Pressures to

produce– FBI arrest of

Muslim attorneyin Portland