This chapter discusses crime scene investigation and evidence collection. It introduces Locard's exchange principle which states that physical evidence is exchanged between a perpetrator and victim/crime scene. It outlines the goals and team members involved in a crime scene investigation. The key steps are securing the scene, separating witnesses, scanning/documenting the scene, searching for evidence, and collecting/packaging evidence maintaining chain of custody. DNA, fingerprints, trace evidence, and other physical/biological evidence can be analyzed to reconstruct the crime.
2. Chapter 2. Crime-Scene Investigation and Evidence
Collection
Introduction
Objectives
Summarize Locard’s exchange principle
Identify four examples of trace evidence
Distinguish between direct and circumstantial evidence
Identify the type of professionals who are present at a crime
scene
Summarize the seven steps of a crime-scene investigator
Explain the importance of securing the crime scene
Identify the methods by which a crime scene is documented
Demonstrate the proper technique in collecting and packaging
trace evidence
Describe how evidence from a crime scene is analyzed
3. Chapter 2. Crime-Scene Investigation and Evidence
Collection
Introduction
A single hair or clothing
fabric can lead police to a
responsible person
The goal of a crime
scene investigation is to
recognize, document,
and collect evidence at
the scene of a crime.
4. Chapter 2. Crime-Scene Investigation and Evidence
Collection
Principle of Exchange
Whenever two people come into contact with each other a physical transfer occurs.
Pet hair on your clothes or rugs
Hair on your brush
Fingerprints on glass
Soil tracked in
A drop of blood
Paint chips
Broken glass
A fiber from clothing
These transferred materials are considered trace evidence.
First noticed by Dr. Edmond Locard
Locard’s Exchange principle states that when a person comes into contact with an
object or another person, a cross-transfer of physical evidence can occur.
Intensity, duration, and nature of the materials can determine extent of transfer.
5. Chapter 2. Crime-Scene Investigation and Evidence
Collection
Types of Evidence
Direct evidence
First hand observation
(eyewitnesses or video)
Confessions
Circumstantial evidence
Indirect evidence, only
actually seen left behind
by the suspect and victim
Can be physical or
biological
6. Chapter 2. Crime-Scene Investigation and Evidence
Collection
Types of Evidence
Examples of Physical
evidence
Fingerprints
Footprints
Shoe prints
Tire impressions
Tool marks
Fibers
Weapons
Bullets
Shell casings
7. Chapter 2. Crime-Scene Investigation and Evidence
Collection
Types of Evidence
Examples of Biological
Evidence
Body fluids
Hair
Plant parts
Natural fibers
Reduces suspects to a
very small number, or
likely individual
8. Chapter 2. Crime-Scene Investigation and Evidence
Collection
Types of Evidence
Trace evidence
Circumstantial evidence
Hair found on a brush,
fingerprints on a glass, blood
drops on a shirt, soil tracked in
to a house on shoes
Class evidence
Narrows an identity to a group
of persons or things
Ex. Blood typing
Individual evidence
Narrows an identity to a single
person or thing.
Ex. Fingerprint
9. Chapter 2. Crime-Scene Investigation and Evidence
Collection
The Crime Scene Investigation Team
Police officers
First to arrive, may need a district
attorney to obtain a search warrant
Crime scene investigators
Document the crime scene, collect
physical evidence, record data,
sketch the scene, and photograph
the scene
Medical examiners (coroners)
Determine time of death when a
homicide occurs
Detectives
Interview witnesses and talk to
crime scene investigators about the
evidence
Specialists
Ex. Entomologists, forensic
scientists, and forensic
psychologist
10. Chapter 2. Crime-Scene Investigation and Evidence
Collection
The Seven S’s of Crime Scene Investigation
1. Securing the scene
2. Separating the
witnesses
3. Scanning the scene
4. Seeing the scene
5. Sketching the scene
6. Searching for evidence
7. Securing and collecting
evidence
11. Chapter 2. Crime-Scene Investigation and Evidence
Collection
Securing the Scene
Securing the scene is the
responsibility of the first responding
police officer (first responder)
Priorities
Safety of all individuals in the area
Preservation of evidence
Transfer, loss, or contamination of
evidence can occur if left unsecured.
Security log will be kept for all those
entering the crime scene
Request any other additional needs.
12. Chapter 2. Crime-Scene Investigation and Evidence
Collection
Separating the Witnesses
Witnesses must not be allowed to
talk to each other
Their accounts must be compared
Prevention of witnesses working
together to create a story
(collusion)
Possible questions:
When did the crime occur?
Who called in the crime?
Who is the victim?
Can the perpetrator be identified?
What did you see happen?
Where were you when you
observed the crime scene?
13. Chapter 2. Crime-Scene Investigation and Evidence
Collection
Scanning the Scene
Scan the scene to
determine where pictures
should be taken.
Determine primary and
secondary scene.
Ex. A murder may have
taken place at one
location (primary scene)
and the corpse found at
another (secondary scene)
14. Chapter 2. Crime-Scene Investigation and Evidence
Collection
Seeing the Scene
Photos of the overall
area and close-up photos
with and without a
measuring ruler should
be taken.
Why is the ruler
necessary?
15. Chapter 2. Crime-Scene Investigation and Evidence
Collection
Sketching the Scene
Note position of body (if any)
and any other evidence
All objects should be measured
from two immovable objects
North should be indicated
Scale should be included
Doors, windows, and furniture
should be included
If outside, trees, vehicles, or
other objects should be
included
Later, a more accurate and final
copy will be created for use in
court.
16. Chapter 2. Crime-Scene Investigation and Evidence
Collection
Searching for Evidence
Four crime scene search
patterns
Grid
Linear
Quadrant or Zone
Spiral
Ensure no area is left
unsearched
May need additional light
sources (example flashlight)
May need the use of forceps
17. Chapter 2. Crime-Scene Investigation and Evidence
Collection
Securing and Collecting Evidence
All evidence needs to be
properly packaged, sealed and
labeled.
Wet evidence must be
dried (prevent the growth
of mold and the
degenerating of DNA)
Evidence is packaged in a
paper bindle.
Placed in a plastic or paper
container, and then sealed
with tape and labeled with the
signature of the collectorAlso
•Name of suspect and victim
•Signature of person recovering the evidence
•Signature of any witnesses present during collection
18. Chapter 2. Crime-Scene Investigation and Evidence
Collection
Packaging Evidence
1. Choose the appropriate-size sheet of clean paper for the
bindle.
2. Crease the paper as shown on page 27.
3. Place evidence in the X location.
4. Fold left and right sides in.
5. Fold in top and bottom.
6. Insert the top flap into the bottom flap then tape close.
7. Place bindle inside a plastic or paper evidence bag.. Fold the
bag closed.
8. Place a seal over the folded edge of the evidence bag.
9. Have the collector write his or her name over the folded edge.
Also, control samples must be obtainted for the purpose of exclusion.
19. Chapter 2. Crime-Scene Investigation and Evidence
Collection
Chain of Custody
Then:
10. The container is given to the next person
responsible for its care.
11. It is taken to the lab to a technician who opens
the packaged for examination at a location
other than the sealed edge.
12. It is repackaged in the original packaging and
is resealed. The technician would then sign
the chain of custody log.
20. Chapter 2. Crime-Scene Investigation and Evidence
Collection
DNA Collection and Packaging
At many crime scenes
DNA evidence can be
the most useful
Why?
21. Chapter 2. Crime-Scene Investigation and Evidence
Collection
DNA Collection and Packaging
The most common places to find DNA evidence are:
Blood
Saliva
Hair
Semen
Also found in:
Urine
Bone
Skin cells
22. Chapter 2. Crime-Scene Investigation and Evidence
Collection
DNA Collection and Packaging
Must identify the victim’s DNA and the DNA of
anyone else who had access to the evidence.
Prosecutors must be prepared for what happens in
court.
If there is any evidence that doesn’t belong to the
suspect, the defense lawyer will try to claim that the
DNA must point to the real perpetrator.
Therefore all DNA must be identified on all of the
evidence to protect the case against the suspect.
23. Chapter 2. Crime-Scene Investigation and Evidence
Collection
DNA Collection and Packaging
DNA evidence needs protection from:
Contamination
Environmental damage
Degredation
24. Chapter 2. Crime-Scene Investigation and Evidence
Collection
Analyze the Evidence
A forensic lab processes all the
evidence from the crime scene.
Lab technicians are specialized and
process one type of evidence.
Results are sent to the lead detective.
A hypothesis can then be formed
(sequence of events)
Evidence can:
Link a suspect with a scene or a
victim
Establish the identity of a victim
or suspect
Confirm verbal witness testimony
Or acquit the innocent
25. Chapter 2. Crime-Scene Investigation and Evidence
Collection
Crime Scene Reconstruction
Crime scene reconstruction involves forming a
hypothesis of the sequence of events from
before the crime was committed through its
commission.
The evidence does not lie, but it could be staged.
26. Chapter 2. Crime-Scene Investigation and Evidence
Collection
Staged Crime Scenes
Examples:
Arson, a perpetrator stages a fire to commit another
crime
Suicide/murder, a victim is murdered and the
perpetrator stages the scene to look like suicide
Burglary, burglary is staged for insurance money
27. Chapter 2. Crime-Scene Investigation and Evidence
Collection
Review
1. Locard’s exchange principle implies all of the
following except:
2. Transfer evidence can include all of the following
except:
3. The reason it is important to separate the witness at
the crime scene is to:
4. Correct collection of evidence requires which of the
following?
5. A crime-scene sketch should include all of the
following except:
b. Blood spatter can be used to identify blood type
a. The victim’s own blood gushing from a wound
c. Prevent the witnesses from talking to each other.
d. All of the above
d. The type of search pattern used to collect evidence