Physical Evidence Prints and impressions (tires, shoes, fingers) \Wrongful arrest,conviction\FBI...
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Transcript of Physical Evidence Prints and impressions (tires, shoes, fingers) \Wrongful arrest,conviction\FBI...
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