Crime Scene Chapter 3

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

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

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

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

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

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

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

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

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

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.
 

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

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)

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

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

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

Thinking Forensically

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

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

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

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)

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

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

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

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