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Evidence
Evidence Definition
• Evidence refers to information or objects that may
be admitted into court for judges and juries to
consider when hearing a case.
Three Types of Evidence
• Testimonial
• A testimony from a witness of a crime
• Physical
• any material items that are present at the crime scene or on
the victims.
• Trace
• Refers to evidence that is found at a crime scene in small
but measurable amounts.
Common Types of Physical Evidence
Drug and toxic substance
Resins, plastics
Fingerprints
Paints
Explosive Residues
Hair
Gun Shot Residues (GSR)
Serial Numbers
Tissues
Firearms and ammunition
Documents
Pollen
Impressions
Fibers
Wood material
Petroleum products
Soil
Feathers
Alcohols (esp. Ethanol)
Glass
Bones
Rubber Material
Blood and Other Body
Fluids
Tool Marks
Evidence and Controls
• Determining the origin of an object or substance
almost always involves a comparison with something
similar or something that scientists know the origin
of, such as a control.
• Evidence is always compared with a known or
control
Types of Physical Evidence
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Trace
Transient
Conditional
Indirect
Circumstantial Evidence
Individual Evidence
Class Evidence
Trace Evidence
• Trace Evidence
• Physical evidence found in small but measureable amounts
• Examples:
• Hairs and fibers
• Skin cells
Locard’s Exchange Principle
The value of trace (or contact) forensic evidence was first recognized
by Edmund Locard in 1910. He was the director of the very first crime
laboratory in existence, located in Lyon, France.
The Locard’s Exchange Principle states that: "with contact
between two items, there will be an exchange."
For example, burglars will leave traces of their presence behind and
will also take traces with them. They may leave hairs from their body
or fibers from their clothing behind and they may take carpet fibers
away with them.
The Atlanta Child Murders (1979 – 1981)
Wayne Williams is thought to be one of the worst serial killers of adolescents in the
U.S. history. His victims were killed and thrown into the Chattahoochee River in
Georgia. Williams was questioned, because he was seen near where a body had
washed ashore. Two kinds of fiber were found on the victims. The first kind was
an unusual yellow-green nylon fiber used in floor carpeting. Through the efforts of
the FBI and DuPont Chemical Company, the carpet manufacturer was identified.
The carpet had been sold in only 10 states, one of them being Alabama, where
Williams lived. Thus the fibers found on the victims were linked to the carpet
fibers found in Williams’ home.
Another victim’s body yielded the second type of fiber. This fiber was
determined to be from carpeting found in pre-1973 Chevrolets. It was determined
that only 680 vehicles registered in Alabama had a matching carpet. Williams
owned a 1970 Chevrolet station wagon with matching carpet. The probability of
both types of fibers being owned by the same person was calculated. The odds
against another person owning both carpet types were about 29 million to one.
Williams was convicted and sentenced to two life terms.
Atlanta Child Murders Reflection
Read The Atlanta Child Murders (1979 – 1981) handout. On a
half sheet of paper answer the following questions. When you
are finished please turn your answers into the basket.
1. Who is Wayne Williams and what did he do?
2. What type of trace evidence was used to convict Wayne Williams?
3. Who assisted the FBI in their investigation?
4. What were the chances of someone owning both types of carpet
types?
5. Do you think this was enough evidence to convict Wayne
Williams?
Trace Evidence and Bindles
• Due to the small nature of trace evidence, it is
usually packaged twice.
• Once in a paper bindle
• Secondly in an envelope or baggie
• A bindle is a paper container.
How to make a bindle
• http://www.iape.org/resourcesPages/iapeDownload
s/WestManheim/bindle.pdf
Transient Evidence
• Transient Evidence
• Temporary evidence that can be easily changed or lost and therefore
must be recorded quickly.
• Examples:
• Odors
• Perfume,, cigarette smoke, gas
• Temperature
• Coffee pot, car hood, water in bath tub, dead body
• Imprints.
• Footprints in sand, fingerprints in dust, teeth marks in perishable food
Conditional Evidence
• Conditional Evidence
• Produced by a specific action or event at the scene and must be
observed and recorded
• Examples
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Lights
Garage door
Doors
Windows
Position of body
Position of furniture
Indirect Evidence
• Indirect Evidence
• Evidence that does not prove or disprove a fact in question
• Evidence providing only a basis for inference about a
disputed fact
• May prove something like the possession of controlled
substances or driving under the influence.
Circumstantial Evidence
• Circumstantial Evidence
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Evidence based on suggestion rather than personal knowledge
implies a fact without actually proving it
The more circumstantial evidence there is the greater it weighs
Probability and statistics are important
• Examples
• blonde hair found in hand of murder victim with black hair
• size 10 sneaker print near the body
Individual Evidence
• Individual Evidence
• Evidence that can be related a single source
• Individualization always involves a comparison
• Narrows an identity to a single person or thing
• Examples
• DNA
• Fingerprints
• Handwriting
Class Evidence
• Class Evidence
• Material that can be associated with a group ofitems that
share properties or characteristics
• Narrows an identity to a group of persons or things
• Examples
• Blood Types
• Hair type
• DNA
Collecting Evidence
How to Collect Evidence
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Search the crime scene for possible evidence
Number or Tag Evidence to be collected
Record the Crime Scene
Properly Record or Bag Evidence
Properly Label all Evidence
Fill out the Chain of Custody
Send to Lab for Analysis
1. Searching For Evidence
• Five Crime Scene Search Patterns
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Grid
Spiral In
Spiral Out
Parallel
Zone
2. Numbering or Tagging Evidence
• Place markers next to the evidence you plan on
collecting.
3. Record the Crime Scene
• Using pictures or a sketch artist
• Use rulers for scale
• Maintains the integrity of the original crime scene
before evidence is moved for analysis.
4. Properly Record or Bag Evidence
• Determine the proper size of baggie or envelope.
• Do not put anything wet into a plastic bag.
• ALWAYS USE PAPER
• Wet things in plastic can grow moldy
• If taking a blood swab sample, always let the sample
dry before packaging it.
• Seal Tightly
5. Properly Record or Bag Evidence
• Always Label Evidence with the Following Number
• Full Name
• Case Number
• Evidence Number
• Date of Collection
• Time of Collection
John. Q. Doe
Case #: 155647
Evidence#: 8
June 16, 1997
4:05 pm
6. Fill out the Chain of Custody
• Chain of custody:
• The documented and unbroken transfer of evidence.
• Whenever you transfer evidence, you must sign a chain of
custody log. This prevents evidence tampering by keeping
track of the evidence at all times.
7. Send to Lab for Analysis
• Return to the lab and begin analyzing the evidence.
• As you do this, you must document and
communicate to other areas of the law as they try to
solve and close the case.