1. Prints and impressions (tires, shoes, fingers)
Physical Evidence
Prints and impressions
(tires, shoes, fingers)
\Wrongful arrest,conviction\FBI Portland case.wmv \DNA and phys evid\church fires tire.wmv

2. Footprint at scene said to Match Avila’s OC Register, 4/5,05
Samantha was kidnapped in July 2002 while playing in front of her home with a friend. Her body was found the next day. She had been sexually assaulted, then suffocated.
Sgt. Robert Kennedy, an RCMP expert on footprint comparison, testified that a footprint found near the body had distinct 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.

3. 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

4. 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

5. Shoes Class characteristics Individual characteristics
Identify brand and model from outsole design features
Computer-assisted matching
Individual characteristics
“Points” of comparison, from questioned to known

6. Tires Class characteristics Identify tire brand and model
Impression in mud compared to suspect’s tire
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

7. Fingerprints What are they? How are they deposited?
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)

8. 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

9. Identification Common patterns Common minutiae Loop Whorl Arch Islands
Island Dot Bifurcation Ridge ending
Common minutiae
Islands
Dots
Bifurcation
Ridge endings
policensw.com

10. 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

11. 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

12. Fingerprint comparison not foolproof
Subjectivity
Sloppy work
Pressures to produce
FBI arrest of Muslim attorney in Portland