Chapter 2 Crime Scene Investigation

Chapter 2. Crime-Scene Investigation and Evidence

Collection

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


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.


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.


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


Types of Evidence Examples of

Physical evidence Fingerprints Footprints Shoe prints Tire impressions Tool marks Fibers Weapons Bullets Shell casings


Types of Evidence Examples of

Biological Evidence Body fluids Hair Plant parts Natural fibers

Reduces suspects to a very small number, or likely individual


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


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


The Seven S’s of Crime Scene Investigation

1. Securing the scene

2. Separating the witnesses

3. Scanning the scene

4. Seeing the scene5. Sketching the

scene6. Searching for

evidence7. Securing and

collecting evidence


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.


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?


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)


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?


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.


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


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 collector

Also• Name of suspect and victim• Signature of person recovering the evidence• Signature of any witnesses present during

collection


Packaging Evidence1. 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.


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.


DNA Collection and Packaging

At many crime scenes DNA evidence can be the most useful

Why?


DNA Collection and Packaging The most common places to find DNA evidence

are: Blood Saliva Hair Semen

Also found in: Urine Bone Skin cells


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.


DNA Collection and Packaging DNA evidence needs protection

from: Contamination Environmental damage Degredation


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


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.


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


Review1. 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

Education

Chapter 2 Crime Scene Investigation