Forensic Science I

1. Chapter 2. Crime-Scene
Investigation and Evidence
Collection

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