The Crime Scene
SFS1. Students will recognize and classify various types of evidence in
relation to the definition and scope of Forensic Science.
b. Distinguish and categorize physical and trace evidence (e.g. ballistics,
drugs, fibers, fingerprints, glass, hair, metal, lip prints, soil, and toxins).
c. Determine the proper techniques to search, isolate, collect, and record
physical and trace evidence.
d. Evaluate the relevance of possible evidence at the site of an
investigation.
e. Organize relevant information to accurately develop and submit both
scene and analysis reports.
ESSENTIAL QUESTIONS
• How can you identify and distinguish
testimonial and physical evidence?
• Why is physical evidence more
valuable?
• How can you identify and distinguish
individual and class evidence?
ESSENTIAL QUESTIONS
• What are the processes involved in
preserving and isolating the crime
scene?
• How do CSIs observe and document a
crime scene, search the scene for
evidence, and collect and package
evidence?
• What is the importance of the chain of
custody?
Types of Evidence
• Testimonial Evidence
– Statement made under oath
– Can be direct or circumstantial evidence
– Juries are heavily influenced by eyewitness
testimony
– Reliability can be questionable
– Hearsay is a statement, other than one made while
testifying, offered in evidence to prove the truth of
the matter
• It is generally inadmissible in criminal court because it is
unreliable, not under oath, and unavailable for crossexamination
Testimonial Evidence
• Witnesses are more accurate in remembering
characteristics such as sex and hair color
rather than age, height, and race
– Witnesses that are physically similar to offender
will be more accurate
– Victims of serious crimes are more accurate
– Presence of a weapon sharpens focus; stress
narrows focus
Testimonial Evidence
• Children usually don’t remember as well as
adults
– Testimony of children is more easily affected by
interviewing techniques
– Older adults, however, have dulled vision and
hearing, resulting in less accuracy
• Learning disabilities, head injury,
drugs/alcohol weaken memory and recall
Testimonial Evidence
• Eyewitnesses are better at answering
questions about the event rather than the
offender’s description
– Open-ended questions get better answers
• Most known cases of an innocent person
being convicted is because of mistaken
eyewitness identification
Types of Evidence
• Physical Evidence
– Any material or object establishing a fact based on
its physical characteristics
– Can be direct or circumstantial
– Generally more reliable than testimonial evidence
– Physical evidence is primarily processed by
comparing a questioned/unknown sample to a
control/known sample.
– Trace evidence is evidence that occurs when
different objects contact one another.
Types of Physical Evidence
• Individual Evidence
– Linked to a unique, single, specific source
– Examples include fingerprints, DNA, broken
pieces, handwriting
• Class Evidence
– Has characteristics common to a group of similar
objects
– Examples include clothing, carpet, food, hair
– Can increase the probative value by using several
pieces to link a suspect to a crime
Physical evidence is valuable
because it can…
• Prove a crime has been committed and set the
scene for the investigation
• Support or refute witness testimony
• Link a suspect with a victim or with a crime
scene
• Determine the identity of people associated
with a crime
• Allow investigators to reconstruct a crime
On scene…
By gathering information at a crime
scene, Crime Scene Investigators can
develop links among the evidence,
victim, crime scene, and perpetrator.
Those links can help them reconstruct
the sequence of events, the modus
operandi, and motive.
Preserving and Isolating
the Crime Scene
• Role of the First Responder
– Determines the nature of the crime
– Gets assistance for the injured
– Detains and/or arrests suspects
– Detains and isolates witnesses
– Secures the crime scene, ensuring all evidence is
contained within the enclosure
– Record all activity
– Remain on site until further staff arrives
Preserving and Isolating
the Crime Scene
• Role of the Medical Examiner
–Note the body’s condition
–Estimate time of death
–Protect physical evidence from
tampering and destruction
Preserving and Isolating
the Crime Scene
• Role of the Investigator
– Interviews victim(s), witnesses, police on
the scene, other specialists
– Responsible for the management of
information given to the press
– Discuss the evidence with the prosecutor’s
office to determine the legal direction of
the investigation
Observing and Documenting
the Scene
• Investigators should examine the
scene to…
–Find possible items of evidence
–Identify entry and exit
–Consider what happened
–Outline how the scene should be
handled
Observing and Documenting
the Scene
• There are three primary methods of
documenting a crime scene
–PHOTOGRAPHY and VIDEO RECORDING
–SKETCHES
–NOTES
Observing and Documenting
the Scene
• PHOTOGRAPHY and VIDEO RECORDING
– Captures important details not immediately
observable
– Scene must be photographed before touching
or moving any evidence
– Should include close-ups of evidence, views
through the eyes of the witness and at various
angles
– Ruler should be used for scale
– Video recordings should begin outdoors and
move indoors
Observing and Documenting
the Scene
• SKETCHES
– Give perspective to the photographs
– Rough sketches are done in situ; finished
sketches are completed using CAD
technology
– Include measurements, scale, relative
placement of all important details in the
crime scene
– Should also include artist’s name,
date/time, reference points, and a legend
Observing and Documenting
the Scene
• NOTES
– One of the most important parts of
processing the crime scene
– Forces investigator to be more observant
and enhances memory of details
– Should include measurements,
names/dates/times, locations,
environmental conditions, description of
crime
– Audio recording can be helpful
Searching the Scene
for Evidence
• The investigators are looking for
anything that should not be there
• Anything that might carry trace
evidence should be collected
• Special lighting may be used to spot
invisible body fluids
• Large search areas may be searched
with multiple investigators
Search Patterns
Collecting and Packaging
Evidence
• All evidence is bagged and labeled
individually
• Reference samples should also be
collected
• Evidence should be sealed with
tamper-proof tape
Maintaining the
Chain of Custody
• Is the chronological documentation
“paper trail” showing the seizure,
custody, control, transfer, analysis, and
disposition of evidence, physical or
electronic.
• The idea behind recording the chain of
custody is to withstand legal challenges
to the authenticity of the evidence.