Chapter 2 Crime-Scene Investigation and Evidence Collection

Chapter 2 Crime-Scene Investigation and Evidence Collection

Multiple Choice

Locard's Principle of Exchange implies all of the following except

• Fibers can be transferred from one person to another.

• Blood spatter can be used to identify blood type.

• Cat hair can be transferred to your pants.

• Soil samples can be carried from the yard into your home.

Multiple Choice

The reason it is important to separate the witnesses at the crime scene is to

• prevent contamination of the evidence.

• prevent fighting among the witnesses.

• prevent the witnesses from talking to each other.

• protect them from the perpetrator

Multiple Choice

Correct collection of evidence requires which of the following?

• Documenting the location where the evidence was found.

• Correct packaging of evidence.

• Maintaining proper chain of custody

• All of these

Multiple Choice

A crime-scene sketch should include all of the following except

• a distance scale

• date and location of the crime scene

• a north heading

• the type of search pattern used to collect the evidence.

Objectives

• Summarize Locard's Principle of Exchange

• Identify four examples of trace evidence

• Distinguish between direct and circumstantial evidence 

• Identify the types of professionals who might be present at a crime scene.

• Summarize the seven steps (7 S's) of a crime-scene investigation

• Explain the importance of securing the crime scene.

• Identify the methods by which a crime scene is documented.
  

Objectives

• Demonstrate proper technique in collecting and packaging trace evidence. 

• Explain what it means to map a crime scene.

• Describe how evidence from a crime scene is analyzed.

Murder or Suicide? 

The 1996 homicide investigation of 6-year old JonBenet Ramsey

provides valuable lessons in proper crime-scene investigation procedures. From this case, we learn how important it is to secure a crime scene. Key forensic evidence can be lost forever without a secure crime scene. 

Goal of CSI

Recognize, document, photograph, and collect evidence at the scene of a crime. Solving the crime depends on piecing together the evidence to form a picture of what happened at the crime scene. 

Multiple Choice

Which of these is not the goal of CSI?

• recognize, document, collect evidence at the crime scene

• arrest and convict the guilty

• solving crimes by piecing together evidence

• interpreting and understanding what happened at the crime scene

Principle of Exchange

Whenever 2 people come into contact with each other or with an object, a physical transfer occurs. 

Trace Evidence

Small but measurable amounts of physical or biological material found at a crime scene.

Examples of trace evidence

• Pet hair on clothes or rugs

• Hair on brushes

• Fingerprints on glass

• Soil tracked into homes or buildings on shoes

• A drop of blood on a shirt

• A used facial tissue

• Paint chips
  

Locard's Principle of Exchange states:

• 1. When a person comes into contact with an object, or another person, a cross-transfer of physical evidence can occur. The exchanged materials indicate that the two entities were in contact. 

• 2. The intensity, duration, and nature of the entities in contact determine the extent of the transfer. For example, more transfer would occur if two individuals engaged in a fist fight than if a person simply brushed past another person. 

In the Ramsey case, 

the police allowed extensive contamination of the crime scene. Police first thought JonBenet had been kidnapped because of a ransom note allegedly found by her mother. For this reason, the police did not search the house until 7 hours after the family called 911. The first responding police officer was investigating the alleged kidnapping, so he did not think to open the basement door and did not discover the body of the murdered girl.

2 Types of evidence

• Direct evidence includes firsthand observations such as eyewitness accounts, police dashboard video cameras, and confessions. 

• Circumstantial evidence is indirect evidence that can be used to imply a fact but that does not prove it. For example, finding a suspect's gun at the site of a shooting is circumstantial evidence of the suspect's presence there. 

Circumstantial evidence 

can be either physical or biological in nature. 

Physical evidence

• fingerprints

• footprints

• shoe prints

• tire impressions

• tool marks

• glass

• soil
  

Biological evidence

• DNA

• Bodily fluids

• hair

• plants

• pollen

• blood

• natural fibers

The Ramsey Case

Believing the crime was kidnapping, the police blocked off JonBenet's bedroom with yellow and black crime-scene tape to preserve evidence her kidnapper may have left behind. But they did not seal off the rest of the house, which was also part of the crime scene. The victim's father, John Ramsey, discovered his daughter's body in the basement of the home. He covered her body with a blanket and carried her to the living room. In doing so, he contaminated the crime scene and may have disturbed evidence. That evidence may have identified the killer. 

Physical evidence 

Most physical evidence , with the exception of fingerprints, reduces the number of suspects to a specific smaller group of individuals. 

Biological evidence

Biological evidence such as blood or DNA may make the group of suspects very small. In the case of DNA, it may reduce the group to a single individual, which is more persuasive in court. 

The Ramsey Case

Once the body was found, family, friends, and police officers remained close by. The Ramseys and visitors were allowed to move freely around the house. One friend helped clean the kitchen, wiping down the counters with a spray cleaner - possibly wiping away evidence. Many hours passed before police blocked off the basement room. A pathologist did not examine the body until more than 18 hours after the crime took place. 

Trace evidence is a type of circumstantial evidence. 

• hair found on a brush

• fingerprints on a glass

• blood drops on a shirt

• Soil tracked into a house

Evidence can also be divided into 

• Class evidence

• Individual evidence

Class evidence

• narrows an identity to a group of persons or things. 

• Knowing the ABO blood type of a sample of blood from a crime scene tells us that one of many persons with that blood type may have been there. 

• It also allows us to exclude anyone with a different blood type. 

Individual evidence 

• narrows an identity to a single person or thing. 

• typically has such a unique combination of characteristics that it could only belong to one person or thing. 

• Fingerprints and DNA

The Ramsey Case

Officers at this crime scene obviously made serious mistakes that may have resulted in the contamination or destruction of evidence. To this day, the crime remains unsolved. 

Open Ended

What are some mistakes made by the Boulder Police Department in the Ramsey case?