CRIME SCENE INVESTIGATION AND

EVIDENCE COLLECTIONBIOLOGY ~ ADVANCED STUDIES

I. Crime Scene InvestigationA. Goals

1. recognize evidence2. document evidence3. collect evidence at a crime

scenea. evidence helps form a picture

of what happened

B. Principle of Exchange 1. physical transfer occurs when

people come in phys. contacta. transferred materials = trace

evidence for forensic examinationb. ex: hair, skin cells, clothing fibers,

pollen, glass, makeup, clothing debris, dirt, blood, etc.

2. Dr. Edmund Locard (1877-1966)

a. 1st forensic lab - Lyon, France; 1910-19121) est. forensic science techniques

still important today b. Locard’s Exchange Principle

1) when a person comes in contact w/an object or another person, a cross-transfer of physical evidence can occur

2) the intensity, duration & nature of the materials in contact determines extent of transfer

a) ex: more transfer in a fist fight than just brushing past someone

C. Types of Evidence 1. 2 main types

a. Direct = 1st hand observations 1) ex: eyewitness account, video,

confessionsb. Circumstantial = indirect

1) used to imply a fact 2) doesn’t directly prove 3) 2 subtypes

a) Physical: incl. fingerprints, footprints, tire impressions, tool

marks, bullets, shell casings, weapons, fibers

b) Biological: incl. body fluids, hair, plant parts, natural fibersc) used to narrow the group of

suspects 1)) biol. often more persuasive

2. Other categories of evidence a. Class: narrows an identity to a group

of persons/things1) ex: blood type of sample collected

b. Individual: narrows identity to a single person or thing1) usually has unique qualities, only

belong to one thing/person2) ex: fingerprint, DNA sample

D. CSI team 1. legal & scientific professionals 2. work at crime scene, at lab, at law

agency & in court 3. personnel at a crime scene:

a. police officers – usually 1st responders to scene

b. crime-scene investigators – record data, sketch & photograph scene, collect evidence

c. Medical examiners – a.k.a. coroner

1) if death, to determine if homicide or natural

d. Detectives – interview witnesses, get evidence info from c.s.i.e. Specialists – if needed for specific

evidence 1) ex: entomologists, psychologists,

other forensic scientists

E. The 7 S’s of CSI 1. Secure the Scene

a. 1st responder’s jobb. 1st priority = safety c. restrict access to scene 1) lessens transfer, loss or

contamination of evidenced. collect pertinent infoe. request needed back-up & experts

2. Separate the Witnesses a. prevents collaboration on accounts of crime

1) each gives a unique perspective b. questions to ask:

1) When did crime occur?2) Who called it in?3) Who’s the victim?4) Do you know who perpetrator is?5) What did you see?6) Where were you when you observed crime scene?

3. Scan the Scene a. forensic examiners determine what

photos to take b. determine if there are primary &

secondary crime scenes 1) assign priorities in examining each

4. See the Scene a. examination by crime scene

examiners b. photos of overall area & close-ups

1) w/ & w/out ruler (for scale)2) incl. stationary objects as

reference points3) taken at several angles4) incl. evidence as well as area

5. Sketch the Scene a. rough sketch at scene 1) noting position of evidence, body 2) indicating North & scale of distance 3) outside, noting position of plants,

buildings, other structures b. later, sketch is made more accurate &

formalized1) may be used as evidence

Rough sketches

Final sketch

6. Search for Evidence a. walk the crime area in a pattern noting

location of evidence1) spiral, grid, linear or quadrant2) ensure all areas are searched

b. may need additional tools to see & collect evidence1) ex: flashlight & tweezers, vacuum w/

clean bag

7. Secure & Collect Evidence a. properly package, seal & label evidence b. specific techniques for collection &

storage vary w/evidence1) liquids, arson remains - airtight,

unbreakable containers

2) moist biol. evidence pack in breathable containers

a) lets it dry & prevents mold b) then, pack dried evidence in a paper

bindle c. seal containers w/ tape & label w/

signature of collector across taped. attach evidence log & chain of custody document to containers

e. packaging evidence techniques 1) choose right size, clean paper for bindle 2) fold to create a packet that totally

surrounds evidence 3) seal & tape paper packet 4) place in plastic or paper evidence bag 5) fold & seal evidence bag 6) collector signs over folded edge

F. Analyzing evidence 1. evidence taken for forensic lab work 2. technicians typically specialize in

processing one type of evidence 3. results can lead to crime-scene

reconstruction

b. Usefulness of evidence 1) link suspects to crime 2) establish witness/suspect i.d.’s 3) confirm witness testimony 4) acquit innocent partiesc. Investigators must be open to all possible evidence interpretations

G. Crime scene reconstruction 1. allows creation of a hypothesis of

the sequence of events from before the crime through its commission

2. includes evidence examination, comparing witness statements, etc.

a. determine how it fits into overall crime scenario

b. see if it’s real or staged

What evidence would you collect from this crime scene?

Make a rough sketch of this crime scene.