Download Chapter 3 Physical Evidence

CHAPTER 3
PHYSICAL EVIDENCE
THE GREEN RIVER KILLER
This case takes its name from the Green River, which flows
through Washington State and empties into the Puget Sound
in Seattle. Within a six-month period span in 1982, the bodies
of five females were discovered in or near the river. Most of
the victims were prostitutes who were strangled and
apparently raped. As police focused their attention on an area
known as Sea-Tac Strip, a haven for prostitutes, girls
mysteriously disappeared with increasing frequency. By the
end of 1986, the body count in the Seattle region rose to
forty; all were believed to have been murdered by the Green
River Killer.
As the investigation pressed into 1987, the police renewed
their interest in one suspect, Gary Ridgway, a local truck
painter. Ridgway had been known to frequent the Sea-Tac.
Interestingly, in 1984 Ridgway actually passed a lie detector
test regarding the Green River killings. Now with a search
warrant in hand, police searched Ridgway’s residence and
also obtained hair and saliva samples from him. Again,
insufficient evidence caused Ridgway to be released from
custody.
THE GREEN RIVER KILLER
With the exception of one killing in 1998, the murder
spree stopped in 1990, and the case remained
dormant for nearly ten years. However, the advent
of DNA testing brought renewed vigor to the
investigation. In 2001, semen samples collected
from three early victims of the Green River Killer
were compared to saliva that had been collected
from Ridgway in 1987. The DNA profiles matched
and the police had their man. An added forensic link
was made by the location of minute amounts of
spray paint on the clothing of six victims that
compared to paints colleted from Ridgway’s
workplace. Ridgway ultimately avoided the death
penalty by confessing to the murders of forty-eight
women.
PHYSICAL EVIDENCE
• Impossible to list all objects that could
conceivably be of importance in a crime
• Every crime has to be treated on an individual
basis!
• Most common types of physical evidence….
All suspected blood, semen, or saliva – liquid or dried,
Blood, Semen, and Saliva animal or human – on fabrics, objects, even cigarette
butts – are subject to serological and biochemical
analysis to determine origin and identity
Documents
Handwriting and typewriting analyzed to determine
authenticity or source. Can also analyze paper, ink,
indented writings, obliterations, and burned, charred
documents
Drugs
Any substance seized in violation of laws regulating sale,
manufacture, distribution, and use of drugs
Explosives
Any device with explosive charge and objects removed
from a scene of an explosion that may contain residues of
an explosive
Fibers
Natural or synthetic fibers whose transfer may be useful
in establishing relationship between objects and/or
persons.
Fingerprints
Latent and visible
Firearms and ammunition
Firearms as well as discharged or intact ammunition
suspected of being involved in a crime
Glass
Glass particle or fragment that may have been
transferred to a person or object involved in a
crime. Includes windowpanes with holes from
bullets or other projectile
Hair
Animal or human hair that can link a person with a
crime
Impressions
Tire markings, shoe prints, depressions in soft
soils, and all forms of tracks. Glove and other
fabric impressions, as well as bite marks in skin or
food.
Organs and physiological fluids
Submitted to detect presence of drugs or poisons,
including alcohol.
Paint
Liquid or dried paint that may have been
transferred from the surface of one object to
another during a crime.
Petroleum products
Most common would be gasoline removed from
an arson crime scene, or grease or oil stains
whose presence may suggest involvement in a
crime
Plastic bags
Disposable bags may be linked to objects
recovered in the possession of a suspect- usually
homicide or drug cases
Plastic, rubber, and other
polymers
May be linked with objects recovered in the possession
of a suspect
Powder Residues
Any item suspected of containing firearm discharge
residues.
Serial Numbers
Stolen property submitted to the lab for restoration of
erased serial numbers.
Soil and minerals
Items containing soil or minerals that could link a person
or objet to a particular location.
Tool marks
Any object suspected of containing the impression of
another object that served as a tool in a crime.
Screwdriver, crowbar impressed or scraped on a wall.
Vehicle lights
Examination of headlight and taillights to determine if
the light was on or off at the time of impact.
Wood and other vegetative
matter
Fragments of wood, sawdust, shavings, or vegetative
matter discovered on clothing, shoes, or tools that could
link a person or object to the crime location.
THE EXAMINATION
OF PHYSICAL EVIDENCE
• The examination of physical evidence by a forensic
scientist is usually undertaken for identification or
comparison.
IDENTIFICATION
• Determine the physical or chemical
identity of a substance with as near
absolute certainty as existing analytical
techniques will permit
• Ultimate identification of a specific
physical or chemical substance to the
exclusion of all other possible
substances
•
•
•
•
Drug analysis
Explosives/gas residues
Species identification
Identification of blood, semen, hair, or wood
(not comparative)
IDENTIFICATION PROCESS
1.
Use testing procedures that give
characteristic results for specific
standard materials
2.
Identification requires that the
number and types of tests
needed to identify a substance
be sufficient to exclude all other
substances
Simple rules cannot be devised for defining what
constitutes a thorough and foolproof analytical
scheme. Each type of evidence requires
different tests and each test has a different
degree of specificity. A substance could be
identified in one test or the combination of 5-6. It
is left to the forensic scientist to determine at
what point the analysis can be concluded and
criteria for positive identification satisfied.
COMPARISON
•
•
The process of ascertaining whether two or more
objects have a common origin
Subjects a suspect specimen to a standard/reference
specimen to the same tests and examinations for the
purpose of determining whether or not they have a
common origin.
Examples –
• Compare hair from crime
scene to hair from suspect
• Compare paint chips on a
hit-and-run victim to
vehicle paint
COMPARISON
1.
Combinations of select properties are chosen from
the suspect and the standard/reference specimen for
comparison
2.
Once the examination has been completed, the
forensic scientist must be prepared to render a
conclusion with respect to the origins of the specimen
If one or more of the properties selected for comparison
do not agree, the analyst may not be able to conclude
that the specimens originated from the same source.
COMPARISON
• To ensure evidential value,
probability is assessed
• Probability - the frequency
or likelihood of occurrence
of an event
Scientists must be able to
ascertain with a high degree
of probability that two or more
specimens are from the same
origin
COMPARISON
1. Individual Characteristics
• Evidence that can be
associated with a common
source with an extremely high
degree of probability (not
possible to state with
mathematical exactness the
specimens are of common
origin)
• Matching ridges of fingerprints
• Striation markings on bullets
• Tool marks
COMPARISON
2. Class Characteristics
•
Inability of the laboratory to
relate physical evidence to a
common origin with a high
degree of certainty but it can
be associated with a group
and never a single source
•
•
Paint
Blood
CLASS CHARACTERISTICS
Product Rule – used to calculate the overall
frequency of an event/occurrence
• Multiply the chances of each part to determine
the probability of all the chances
For example – O.J. Simpson Blood (p.84)
• Multiply the probability of his blood components and determine the
likelihood of his presence
• Probability – 0.26 x 0.85 x 0.02 = 0.0044 or 0.44% match (1 in 200)
Blood Factors
Frequency
A
26%
EsD
85%
PGM 2+2-
2%
SIGNIGICANCE OF
PHYSICAL EVIDENCE
• Most items of physical evidence retrieved at a crime scene
cannot be linked definitely to a single person or object
• The value of class evidence lies in its ability to corroborate
events with data in a manner that is free of human error or
bias (as much as possible)
• As the number of different objects linking an individual to a
crime scene increase, so does the likelihood of that
individual’s involvement with the crime
• The weight or significance accorded physical evidence is
determined by the jury in a trial
• Physical evidence can also exonerate a person from
suspicion
FORENSIC DATABASES
Database
Purpose
Integrated Fingerprint Identification
System (IAFIS)
•
Combined DNA Index System
(CODIS)
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•
•
•
•
•
National Integrated Ballistics
Information Network (NIBIN)
•
International Forensic Automotive
Paint Data Query (PDQ)
•
•
•
National fingerprint and criminal history
system
Maintained by FBI since 1999
Contains nearly 50 million subjects form
local, state, and federal agencies
Maintained by 1998 by the FBI
DNA samples submitted form local, state,
and federal laboratories
All states submit DNA of felony sexual
offenders
Contain sources of DNA from unsolved
crime as well as convicted criminals
Maintained by Bureau of Alcohol. Tobacco,
Firearms, and Explosives
Images of bullets and cartridge cases
recovered from crime scenes
Chemical and color information to original
auto paints
Information on make, model, year, and
assembly plant
CRIME-SCENE RECONSTRUCTION
• Efforts to reconstruct events that occurred prior, during, and
subsequent to the crime
• Was there more than one person involved?
• How was the victim killed?
• Were there actions taken to cover up what actually took place?
• Crime scene reconstruction relies on the combined efforts of
medical examiners, forensic scientists, and law enforcement
personnel to sort out the events surrounding the occurrence of
a crime.
• Reconstruction supports a likely sequence of events by the
observation and evaluation of physical evidence as well as
statements made by witnesses and those involved with the
incident
• Only accomplished when a crime scene has been properly
processed and recorded and physical evidence has been
collected
• Examples:
• Determine if body was moved
• Analyze bullet trajectory
• Analyze blood spatter
• Determine direction of projectiles hitting glass
• Estimate distance of a shooter