1. Crime Scene
Chapter 3

2. Crime scene First official on scene (usually responding officer):
1st priority: people safety (check pulse!)
2nd priority: secure the scene--keep people from altering evidence
3rd priority: detain suspects/witnesses

4. Questions
Ask ASAP
Question the 1st on scene and witnesses about any transient evidence:
Weather, odors, visibility, points of entry/exit

5. Crime scene process #1: Safety #2: Secure the scene
Talk to witnesses/suspects
Note transient evidence
#3: Preliminary survey (boundaries, exits)
Narrative, photograph, sketch
#4: Detailed search
Continue Narrative, photograph, sketch
Collect evidence
#5: Maintain chain of custody
#6: Final survey – release crime scene

6. Preliminary Survey
From outside the crime scene: do not know boundaries of crime scene
body may have been dragged
drugs may have been dropped while fleeing the scene

7. Preliminary Survey Narrative: Detailed and legible (NEAT!)
Acts as a timeline
Describe time of day, weather, lighting (transient info)
Written description of physical evidence
Names of people involved

8. Preliminary Survey Photograph Before touch or move anything
Take photos from different angles
Have ruler for scale
Photo from outside to inside in order
Photograph each piece of evidence individually- and from far away

14. Preliminary Survey Sketch: MUST INCLUDE a key - scale - compass
Original sketch is evidence in case
Scale: gives relationship of sketch to actual size
Key: explains code used in sketch
Compass: for orientation

18. Detailed survey From within the crime scene Photograph Sketch
Narrative
Collect evidence
Initiate chain of custody

19. Chain of custody: a list of all persons who came into possession of an item of evidence

20. Custody Samples and data are considered to be in your custody when
they are in your physical possession
they are in your view, after being in your physical possession
they are in your physical possession and then locked up so that tampering cannot occur
they are kept in a secured area, with access restricted to authorized personnel only.
 

21. Chain of custody
Keep the number of people involved in collecting and handling samples and data to a minimum:
Always document the transfer of samples and data from one person to another on chain-of-custody forms

23. Collection of evidence
Wet items: dry them, package them in paper to prevent molding
Biological items: freeze them
Fire arms: locked inside wooden container
Fumes (arson): kept in airtight container
Collect most delicate items first during preliminary survey (transient evidence)

28. What’s the difference?
Identification: the process of determining a substance’s physical or chemical identity
Comparison: the process of figuring out whether two or more objects have a common origin

29. The Role of Forensic Science
Provide scientific information to the legal community with reports and testimony
A statement of the LIMITATIONS of the science!

30. Responsibility of the Analyst
Must use scientific method. Experimental design
Work must be reproduceable, other scientists shoul get same results
Must report the limitations or percent error

31. Thinking Forensically

32. Fundamental Principles
Transfer
Locard Exchange Principle
Identification
placing objects in a class
Individualization
narrowing the class to one

33. The Locard Exchange Principle
Whenever two objects come into contact, there is always a transfer of material

34. Transfer Physical movement of material from one place to another
1 mm fiber transferred from a sweater (its source) to a sweatshirt (its destination) during contact

35. Imprint: not considered a transfer!
No physical movement of material
a pattern formed when an object makes an impression
shoe stepping in mud
(no detectable amount of leather left by shoe)

36. Class Evidence- Review
Once an object is identified by class, the object can be compared to a reference (CONTROL SAMPLE) item
determine if it came from that source or some other
If so, it can be used as circumstantial evidence against the suspect

37. Individual Evidence: Review
Accomplished by examining traits that are unique to a source item

38. Individualizing Traits: Examples
Minutiae of friction ridges on fingers (fingerprints)
nicks, cuts or gouges in a tire
DNA

39. Individualizing Characteristics
If two objects possess individualizing characteristics so that the analyst can conclude that no other items exhibit the same traits
Example: latent print at crime scene and a reference set of prints made at the police station