Unit 1: Target 3.1-3.7

Crime scene investigators

Trained to recognize, document, photograph, and collect all forms of evidence at a crime scene

Is it possible for a crime to be committed without the perpetrator leaving behind some type of evidence

It’s impossible

Crime scene investigation

Recognize, document, photograph, and collect evidence at the scene of the crime

What must the evidence be in order for it to be able to be used in court

• Reliable

• Valid

What must evidence be

• Scientific

• Objective

• Properly collected

CSI team

Made of legal and scientific professionals that work together to solve a crime

List the 6 members of a CSI team

• Police officers

• District attorneys

• CSI’s

• Medical examiners

• Detectives

• Specialists

Police officers

• First at scene

• Work to secure scene

• Trained in basic forensics

District attorneys

Determine if search warrant is necessary

CSI’s

• Document the crime scene in detail

• Collect evidence

Medical examiners

Determine manner of death

Detectives

Interview witnesses, CSI’s, and specialists to get evidence that helped to construct the crime scene

Specialists

Only called in if needed

List the 3 examples of a specialist

• Forensic pathologists

• Botanists

• Entomologists

Forensic pathologists

Identify remains

Botanists

Determine time of year or region through plants

Entomologists

Estimate the post mortem interval or time of death

Locard’s principle of exchange

• Whenever 2 people come into contact with eachother or with an object a physical transfer occurs

• Indicates 2 people or objects were in contact with each other

• The more intense or longe the exchange, the more evidence will be transferred

Trace evidence

Transferred materials between people or objects

List the 2 types of evidence

• Direct evidence

• Circumstantial evidence

Direct evidence

First hand observations such as eye witness accounts or police dash board cameras

Circumstantial evidence

• Indirect evidence used to imply a fact, but does not prove it

• May give a link between a crime scene and suspect but doesn’t prove that the suspect did the crime

Physical evidence

• Finger prints

• Shoe prints

• Tire imprints

• Tool marks

• Fibers

• Weapons

Biological evidence

• DNA tissue

• Bodily fluids

• Hair

• Plants

• Pollen

• Natural fibers

Class evidence

• Narrows the identity to a group of people or things

• Example: Finding a certain blood type narrows the suspect list down to those who have that type, and eliminates those with other blood types

Individual evidence

Narrows the search down to a single individual to show it only belongs to one person

List the 7 S’s of crime scene investigation

• Secure the scene

• Separate the witnesses

• Scan the scene

• See the scene

• Sketch the scene

• Search for evidence

• Secure and collect evidence

Secure the scene

• Responsibility of the first responder or law enforcement

• Safety of individuals is the first priority, followed by the preservation of evidence

• Protect the area where the crime has occurred, restrict all unauthorized individuals

• Prevent scene contamination

Separate the witnesses

• Keeping the witnesses separated prevents them from working together to create a story

• Witnesses are asked a series of questions:

  • When did the crime occur?

  • Who notified law enforcement?

  • Who is the victim?

  • Can the perpetrator be identified?

  • What did you see happen?

  • Where were you when you observed the crime scene?

Scan the scene

• By scanning the scene, a CSI can determine where photos should be taken

• Determine the primary crime scene (The location of the crime) and secondary crime scene (The location where additional evidence may be found)

See the scene

• Take photos of the area, both overall and close-up photos

• Using measuring rulers and reference points to compare photos

• Triangulation is used which is a technique used to record evidence location from two fixed reference points

• Use photos from many locations and angles

Sketch the scene

• CSI makes an accurate sketch of the scene and notes evidence and remains

• North should be identified and distance scale provided

• All objects should be measured and structures drawn accurately

• Specialized software can later make a detailed image for use in court

Search for evidence

• CSI searches the area in a systematic way to make sure the whole area is covered

• Patterns of search include grid, linear, quadrant/zone, and spiral

• All evidence should be photographed, sketched, labeled, and documented

Secure and collect evidence

• All evidence needs to be properly packaged, sealed, and labeled

• Liquids and arson remains stored in airtight, unbreakable containers

• Biological evidence stored in breathable containers to prevent mold

• Evidence is placed into a paper bindle, then a container, sealed, and labeled

• Chain of custody is recorded where each handler signs and documents transfer