1. Chapter 2 Crime Scene Investigation and Evidence Collection By the end of this chapter you will be able to:
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
Describe how evidence from a crime scene is analyzed
All Rights Reserved South-Western / Cengage Learning © 2012, 2009
Forensic Science: Fundamentals & Investigations, Chapter 2

2. Chapter 2 Crime Scene Investigation and Evidence Collection By the end of this chapter you will be able to:
Summarize the three steps of a crime scene investigation
Explain the importance of securing the crime scene
Identify the methods by which a crime scene is documented
Demonstrate proper technique in collecting and packaging trace evidence
Forensic Science: Fundamentals & Investigations, Chapter 2

3. Principle of Exchange
Established by Dr. Edmond Locard, the principle states:
When a person comes in contact with an object or another person, a cross-transfer of physical material can occur
Study of the material can determine the nature and duration of the transfer
“Locard’s Exchange Principle”
Forensic Science: Fundamentals & Investigations, Chapter 2

4. Types of Evidence Direct evidence
Testimony by a witness about what that witness saw, heard, or did
(Eyewitness Testimony – has probative value)
Probative value: the ability of evidence to prove something that is material to a crime
Forensic Science: Fundamentals & Investigations, Chapter 2

5. Types of Evidence Circumstantial evidence Physical evidence
also called Indirect
trace evidence
Has PROBATIVE Value
Physical evidence
e.g., fingerprints
Biological evidence
e.g., blood or hairs
Forensic Science: Fundamentals & Investigations, Chapter 2

6. Types of Evidence Explain why this would be or
would not be trace evidence
Forensic Science: Fundamentals & Investigations, Chapter 2

7. Reliability of Eyewitness (Direct Evidence – Testimonial Evidence)
Factors:
Nature of the offense and the situation in which the crime is observed
Characteristics of the witness
Manner in which the information is retrieved
Additional factors:
Witness’s prior relationship with the accused
Length of time between the offense and the identification
Any prior identification or failure to identify the defendant
Any prior identification of a person other than the defendant by the eyewitness
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8. Eyewitness
A police composite may be developed from the witness testimony by a computer program or forensic artist.
“Perception is reality.”
As a result of the influences in eyewitness memory, physical evidence becomes critical.
Faces—a composite program
by InterQuest
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9. Value of Physical Evidence
Generally more reliable than testimonial
Can prove that a crime has been committed
Can corroborate or refute testimony
Can link a suspect with a victim or with a crime scene
Can establish the identity of persons associated with a crime
Can allow reconstruction of events of a crime
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10. Reconstruction Physical Evidence is used to answer questions about:
what took place
how the victim was killed
number of people involved
sequence of events
A forensic scientist will compare the questioned or unknown sample with a sample of known origin.
(From Suspects
and victim)
(Found at the Crime scene)
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11. Types of Physical Evidence
Transient Evidence—temporary; easily changed or lost; usually observed by the first officer at the scene
Pattern Evidence—produced by direct contact between a person and an object or between two objects
Conditional Evidence—produced by a specific event or action; important in crime scene reconstruction and in determining the set of circumstances or sequence within a particular event
Transfer Evidence—produced by contact between person(s) or object(s), or between person(s) and person(s)
Associative Evidence—items that may associate a victim or suspect with a scene or each other; ie, personal belongings
—Lee and Labriola in Famous Cases, 2001
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12. Examples of Transient Evidence
Odor—putrefaction, perfume, gasoline, urine, burning, explosives, cigarette or cigar smoke
Temperature—surroundings, car hood, coffee, water in a bathtub, cadaver
Imprints and indentations—footprints, teeth marks in perishable foods, tire marks on certain surfaces
Markings
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13. Examples of Pattern Evidence
Pattern Evidence—most are in the form of imprints, indentations, striations, markings, fractures or deposits.
Clothing or article distribution
Gun powder residue
Material damage
Body position
Tool marks
Modus operandi (M.O.)
Blood spatter
Glass fracture
Fire burn pattern
Furniture position
Projectile trajectory
Tire marks or skid marks
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14. Examples of Conditional Evidence
Light—headlight, lighting conditions
Smoke—color, direction of travel, density, odor
Fire—color and direction of the flames, speed of spread, temperature and condition of fire
Location—of injuries or wounds, of bloodstains, of the victim’s vehicle, of weapons or cartridge cases, of broken glass
Vehicles—doors locked or unlocked, windows opened or closed, radio off or on (station), odometer mileage
Body—position, types of wounds; rigor, livor and algor mortis
Scene—condition of furniture, doors and windows, any disturbance or signs of a struggle
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15. Classification of Evidence by Nature
Biological—blood, semen, saliva, sweat, tears, hair, bone, tissues, urine, feces, animal material, insects, bacterial, fungal, botanical
Chemical—fibers, glass, soil, gunpowder, metal, mineral, narcotics, drugs, paper, ink, cosmetics, paint, plastic, lubricants, fertilizer
Physical—fingerprints, footprints, shoe prints, handwriting, firearms, tire marks, tool marks, typewriting
Miscellaneous—laundry marks, voice analysis, polygraph, photography, stress evaluation, psycholinguistic analysis, vehicle identification
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16. Evidence Characteristics
Class—common to a group of objects or persons (low probative value-can help to prove something)
Individual—can be identified with a particular person or a single source (high probative value)
Fingerprints
Blood DNA Typing
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17. Class vs Individual Evidence
Which examples do you think could be individual evidence?
Does class evidence help to prove anything? “the value of class evidence”
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18. Class vs Individual Evidence
These fibers are class evidence—there are millions like them.
The large piece of glass fits to the bottle—it is individual evidence
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19. The Crime Scene Investigation Team
Who is at the crime scene?
Police and
District attorney (possibly)
Crime scene investigators
Medical examiners
Detectives
Specialists
Forensic Science: Fundamentals & Investigations, Chapter 2

20. The Seven S’s of Crime Scene Investigation
Secure the scene (Seek Medical Attention 1st Preserve evidence 2nd)
Separate the witnesses
Scan the scene (Detailed observ. & notes)
Seeing the scene (Photographs)
Sketch the scene (Rough & Final Sketch)
Search for evidence
Secure the collected evidence
** See additional notes/activities**
Forensic Science: Fundamentals & Investigations, Chapter 2

21. Crime-Scene Sketch Form
Forensic Science: Fundamentals & Investigations, Chapter 2

22. Crime-Scene Search Patterns
Pattern used depends on: Number of investigators & size of area
Single investigator – grid, linear or spiral
Group of investigators – linear, zone or quadrant
Patterns are systematic and ensures that no area is left unsearched
Forensic Science: Fundamentals & Investigations, Chapter 2

23. Packaging the evidence
Crease a clean paper and place evidence in the X position
Fold in the left and right sides, and then fold in the top and bottom
Put the bindle into a plastic or paper evidence bag affixing a seal over the opening
Write your name on the seal
Forensic Science: Fundamentals & Investigations, Chapter 2

24. Evidence ID Forms
Forensic Science: Fundamentals & Investigations, Chapter 2

25. Chain of Custody
Maintaining a chain of custody log is essential to present credible evidence in court
Forensic Science: Fundamentals & Investigations, Chapter 2

26. Chain of Custody (cont’d.)
Bag the evidence Add identification Seal it Sign it across the sealed edge
Sign over to a lab technician Open bag on non-sealed edge
Return items to the evidence bag Seal evidence bag in another bag Sign the evidence log
Forensic Science: Fundamentals & Investigations, Chapter 2

27. Analyze the Evidence
Facts result from collected evidence processed by the forensic lab
Lead detective aims to see how facts fit into the crime scenario
Forensic Science: Fundamentals & Investigations, Chapter 2

28. Analyze the Evidence Lab results can:
Show reliability of witness accounts
Establish the identity of suspects or victims
Show suspects to be innocent or link them with a scene or victim
Forensic Science: Fundamentals & Investigations, Chapter 2

29. Crime Scene Reconstruction
Crime scene reconstruction involves:
Forming a hypothesis of the sequence of events
From before the crime was committed through its commission
Means? Motive? Opportunity?
Forensic Science: Fundamentals & Investigations, Chapter 2

30. Staged Crime Scenes
When lab results don’t match up with the testimony of witnesses
Common examples:
Staging a fire—to cover bankruptcy
Staging a suicide—to cover a murder
Staging a burglary—to collect insurance money
Forensic Science: Fundamentals & Investigations, Chapter 2

31. Staged Crime Scenes Was the crime scene staged? Consider:
Does the type of wound match the weapon?
Could the wound be easily self-inflicted?
What were the mood and actions of the victim before the event?
What were the mood and actions of the suspect before the event?
Forensic Science: Fundamentals & Investigations, Chapter 2

32. Summary
Locard’s exchange principle:
Contact between people and objects can transfer material that can determine the nature and duration of the transfer
Evidence can be direct or indirect
Physical or biological traces
A crime scene investigation team consists of police, detectives, crime scene investigators, medical investigators, and specialists.
Forensic Science: Fundamentals & Investigations, Chapter 2

33. Summary
Investigations consist of recognizing, documenting, and collecting evidence.
First responding officers identify the extent of the crime scene, secure it, and segregate witnesses.
Crime scene investigators document the crime scene.
Evidence is collected, packaged, and labeled.
The evidence is analyzed and interpreted to fit the crime scenario.
Forensic Science: Fundamentals & Investigations, Chapter 2