1. Crime Scene Basics Forensic Science
T. Trimpe

2. Crime Scene Vocabulary
CRIME SCENE: Any physical location in which a crime has occurred or is suspected of having occurred.
PRIMARY CRIME SCENE: The original location of a crime or accident.
SECONDARY CRIME SCENE: An alternate location where additional evidence may be found.
SUSPECT: Person thought to be capable of committing a crime.
ACCOMPLICE: Person associated with someone suspected of committing a crime.
ALIBI: Statement of where a suspect was at the time of a crime.
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3. What will evidence collected at a scene do for the investigation?
Types of Evidence
Testimonial evidence includes oral or written statements given to police as well as court testimony by people who witnessed an event.
Physical evidence refers to any material items that would be present at the crime scene, on the victims, or found in a suspect’s possession.
Trace evidence refers to physical evidence that is found in small but measurable amounts, such as strands of hair, fibers, or skin cells.
What will evidence collected at a scene do for the investigation?
May prove that a crime has been committed
Establish key elements of a crime
Link a suspect with a crime scene or a victim
Establish the identity of a victim or suspect
Corroborate verbal witness testimony
Exonerate the innocent.
Give detectives leads to work with in the case
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4. Crime Scene Personnel
POLICE OFFICERS are typically the first to arrive at a crime scene. They are responsible for securing the scene so no evidence is destroyed and detaining persons of interest in the crime.
The CSI UNIT documents the crime scene in detail and collects any physical evidence.
The DISTRICT ATTORNEY is often present to help determine if any search warrants are required to proceed and obtains those warrants from a judge.
The MEDICAL EXAMINER (if a homicide) may or may not be present to determine a preliminary cause of death.
SPECIALISTS (forensic entomologists, anthropologists, or psychologists) may be called in if the evidence requires expert analysis.
DETECTIVES interview witnesses and consult with the CSI unit. They investigate the crime by following leads provided by witnesses and physical evidence.
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5. Adapted from http://www.feinc.net/cs-proc.htm
Crime Scene Protocol
Step 1: Interview
The first step in investigating a crime scene is to interview the first officer at the scene or the victim to determine what allegedly happened, what crime took place, and how was the crime committed. This information may not be factual information but it will give the investigators a place to start.
Step 2: Examine
The second step in the investigation of a crime scene, which will help identify possible evidence, identify the point of entry and point of exit, and outline the general layout of the crime scene.
Step 3: Document
The third step in the protocol involves creating a pictorial record of the scene as well as a rough sketch to demonstrate the layout of the crime scene and to identify the exact position of the deceased victim or other evidence within the crime scene.
Step 4: Process
This is the last step in the protocol. The crime scene technician will process the crime scene for evidence, both physical and testimonial evidence. It is the crime scene technicians responsibility to identify, evaluate and collect physical evidence from the crime scene for further analysis by a crime laboratory.
Adapted from

6. PROCESSING A CRIME SCENE
Isolate and secure the scene
Document the scene
Search for evidence
Collect and package evidence, maintaining the chain of custody
Submit evidence to the crime lab

7. Top Reasons for Committing a Crime
Money
Revenge
Emotion—love, hate, anger
Source of Evidence
Body
Primary and/or Secondary Crime Scene
Suspect(s)
Kendall/Hunt Publishing Company

8. Locard’s Exchange Principle
States that with contact between two items, there will always be an exchange. This is the basis of trace evidence collection at a crime scene.

9. Physical Evidence Any object or material found
As large as building, as small as hair…odor and submicroscopic like DNA
Unique to crime
Generally more reliable than testimony

10. Value of Physical Evidence
Can prove crime was committed
Support or reject witness testimony
Link suspect with victim or crime scene
Determine identity of people involved in crime
Allows investigators to re-create crime

11. Evidence –
class or individual?

12. Individual Evidence Best type of evidence
Anything that can be linked to a unique/individual source
Ex:
Fingerprints
DNA pattern
Handwriting
Broken glass that fits together

13. Class Evidence Most evidence fits in this category
Object has characteristics common to a group of objects
Ex:
Blue jeans
Even despite the different sizes, shades, and brand
there are still thousands of pairs just like them
BUT – tears, stains, creases, patches can individualize them

14. Probative Value
Definition: Ability of evidence to prove something that is material to crime
Probative means supplying proof or evidence
How can you increase probative value of class evidence???
Get as many different types of objects as possible to link the suspect to the crime or victim
What’s the probative value of class evidence vs. individual evidence???

15. Step 1
The first officer to arrive at the scene is responsible for securing the crime scene.
Priorities should be:
Medical assistance for individuals in need
Arresting the perpetrator
Protect crime scene
Exclude all unauthorized personnel from the scene.
Communicate to crime scene investigators all movements and alterations made to the scene.

16. Step 2 Preliminary Examination Documenting the crime scene
“Walk-through”
Documenting the crime scene
Videotaping, Photography, Sketches, and Notes are the four methods for crime- scene recording
Ideally all four should be employed; however, as is often the case, personnel and monetary limitations may prohibit the utilization of some.

17. Photography Must be in an unaltered condition Overview photographs
Unless there are injured parties involved, objects must not be moved until they have been photographed from all necessary angles.
As items of physical evidence are discovered, they are photographed to show their position and location relative to the entire scene.
Midrange photographs
Close-ups photographs
When the size of an item is of significance, a ruler or other measuring scale may be inserted and included as a point of reference.

18. Sketching in relation to Photography
A sketch can:
Depict entire scene in one visual whereas a photograph cannot
Be selective & eliminate distracting confusion
Record spatial relationship between items
Sketches may give a better overall layout of the scene than do photos.

19. Types of Sketches Types of Sketches: **Overhead
Most common, overhead view, type we will do
Cross projection or exploded view
Cut apart walls like a box & lay flat
Elevation
View from eye level
Perspective
3D photograph-like

21. Sketches
Rough Sketch —A draft representation of all essential evidence
information and measurements are taken
drawn at the crime scene
Shows all recovered items of physical evidence
Important features of the crime scene (entry, exits, etc)
Finished Sketch —A precise rendering of the crime
drawn to scale
not normally completed at the crime scene
drawn with care and concern for aesthetic appearance

23. Rough sketch should include:
Preparer’s Name
Date and Time
Compass direction
Objects/evidence
Measurements of rooms, windows, doors & furniture
Distances between objects, bodies, persons & entrances/exits
Key/legend

24. Procedure for sketching
Measure all distances
inches used
Measure walls, windows, door, furniture, people, guns, shoe prints, etc.
Triangulation method:
There are 3 points of measurement: item of evidence & 2 fixed objects
Triangle is created when measurements are made from each of the 2 fixed points to item of evidence
Rectangular Coordinate Measurements
Measure from 90 degree angle of 2 points

26. Notes Must be a constant throughout the processing of the crime scene
Should include:
Detailed written description of the scene
location of items of physical evidence recovered
Time and by whom evidence was discovered
How and by whom evidence was packaged
May be the only way to refresh one’s memory of the crime scene

27. Importance of Recording
Only a limited amount of time in untouched state
Opportunity to record original state is key
Important for:
Investigation
Presentation at a trial

28. SEARCH METHODS Line or strip method—best in large, outdoor scenes
Grid method—basically a double-line search; effective, but time-consuming
Zone method—most effective in houses or buildings; teams are assigned small zones for searching
Wheel or ray method—best on small, circular crime scenes
Spiral method—may move inward or outward; best used where there are no physical barriers
Kendall/Hunt Publishing Company

29. Search Methods

30. The Search
Often, many items of evidence are clearly visible but others may be detected only through examination at the crime laboratory.
For this reason, it is important to collect possible carriers of trace evidence, such as clothing, vacuum sweepings, and fingernail scraping

31. Autopsy
Search for physical evidence must extend beyond the crime scene to the autopsy room
The medical examiner or coroner
examine the victim to establish a cause and manner of death
Tissues and organs will be retained for
pathological examination
toxicological examination

32. Physical evidence collected from body
Victim’s clothing
Fingernail scrapings
Hairs
Blood (for DNA typing purposes)
Body Swabs (in sex related crimes)
Recovered bullets from the body
Hand swabs from shooting victims(for gunshot residue analysis)

33. Packaging Evidence
Each item collected at different locations must be placed in separate containers.
Prevents damage through contact and prevents cross-contamination.
Manilla envelopes, pill bottles, twist on cap glass bottles, paper (using “druggist fold”)
Bloodstained materials stored in airtight containers
may encourage the accumulation of moisture and the growth of mold, which can destroy the evidential value of blood.
In these instances, wrapping paper, manila envelopes, or paper bags are recommended packaging materials.

34. Chain of Custody
Chain of Custody—A list of all persons who came into possession of an item of evidence.
Important for court
Adherence to standard procedures is critical to chain of custody.
Recording the location of evidence
Marking it for identification
Properly completing evidence submission forms for laboratory analysis
**Every person who handled or examined the evidence and where it is at all times must be accounted for.