Forensics Chapter 2 & 3

Locard priniciple

When two items come into contact, there is a transfer of material

Evidence

• Something that proves or disproves a fact, physical or testimonial

• Type of evidence depends on type of crime

• Forensic scientist’s main job is to collect and analyze evidence

Why is evidence important?

• Prove a crime has been committed

• Support/refute witness testimony

• Establish the guilt or innocence of possible suspects

• Link suspect and victim/crime scene

• Identify people (DNA, fingerprints)

• Reconstruct the crime 

• Link crimes

2 types of evidence

• Physical and testimonial

• Physical evidence is more reliable than testimonial

Circumstantial evidence

• requires the jury to draw a conclusion that some relevant fact occurred

• inference, suggestion

• Ex. Jake is accused of robbing a store. A piece of evidence is that his phone GPS shows he was near the store. There is a step of making an inference so it’s circumstantial

Transient

• Temporary, easily changed, lost

• Odor, temperature (coffee pot, bathtub water, car hood, body), smoke, imprints and indentations

Pattern

• Blood spatter, glass fracture, tire marks, gun powder residue

Conditional

• Produced by a specific event or action

• Lights (on/off), doors/windows (open/closed), position of body, furniture, other evidence, vehicles

Transfer

• Produced by contact between people, objects

Associative

• Something that may associate a victim or suspect with a scene or with each other

• Necklace , id, credit card, picture

Classifications of physical evidence

• Biological: blood, saliva, sweat, hair, bones, urine

• Chemical: drugs, gun powder, ink, minerals, poisons

• Physical: footprints, handwriting, toolmarks, firearms

• Miscellaneous: voice analysis, Polygraph results

Types of evidence samples

• Unknown/questioned sample:

  • Collected from a known location but is of unknown origin

  • Collected from crime scene 

• Known Sample

  • Comes from a proven or known source 

• Control Sample 

  • Material that is expected to respond in particular way in testing

  • Similar to questioned and known samples 

  • Validates the test

Class vs. individual evidence

• Individual: Can be identified as belonging to a particular person or a single source, 1 person

• Class: Common to a group of objects or persons, more than 1 person

Crime Scene

Any place where evidence may be located or collected (not just where a dead body is located)

Steps for perserving & isolating the crime scene

• First officer:

  • Offering medical assistance

  • Make arrest

  • Protect & secure crime scene, using crime scene tape

  • Detain witnesses and suspects

• Walk through: First officer, CSI, lead detective

  • Explanation on what happened

  • Note any transient or conditional evidence

  • Note points of entry and exits

  • Safety concerns

• Medical Examiner 

  • BODY → Collect all evidence + examine time of death

  • Only this person can confirm whether the person is dead or not

Before entering the crime scene steps

• Sign entry log when entering crime scene (important, if not signed in or out, evidence can’t be used)

• Take a good look from the outside

• Take note of anything suspicious 

• Gloves on, foot covers on, full body cover, etc..

• Carefully enter crime scene 

  • Sign exit log when you leave

Things to do when searching the scene

Mark

• Anything related to crime 

• Trace evidence 

• Collect more evidence than needed:

  • Only allowed to collect evidence once, can’t go back to the crime more than once for collecting 

• Done systematically 

• Evidence log

Searching scene methods

• Line:

  • Outside

  • Shoulder to shoulder

• Grid:

  • Double line 

  • Used for bigger rooms with nooks and crannies (ex. Our school cafeteria)

• Zone:

  • Houses/buildings

• Wheel/Spiral: 

  • Inward or outward in a spiral pattern

  • Used for smaller spaces

Things to do when observing & documenting the scene

• Note the date, time, location, people involved, making it rlly detailed

• Evidence, entry/exit, sequence of events

• Tape record

• Oblique lighting 

  • Shine a light at an angle to reveal evidence

  • UV light

Things to do when documenting the scene

• Photographing of evidence:

  • Before touching and/or collecting evidence take pictures 

  • Must include ruler and marker, the ruler is used to show the size of the evidence/object

  • Close up + mid-range shots for each subject piece of evidence 

  • Photos as viewed by witness, suspect, or victim

• Video: 

  • Allows for narration

• Sketches:

  • Provides perspective to photographs

  • Measurements

    • To scale 

    • 2 points of reference for each  piece of evidence 

  • Includes evidence in sketch 

  • ENtrances + exits

• Final sketch 

  • Date + Tine

  • Scale

  • Key 

  • Measurements 

  • Name of sketcher

Things to do when collecting & packaging evidence

• Have gloves on: Need a new pair for each piece of evidence to reduce cross contamination

• Use things like tongs, tweezers, scoopula, swabs

• Keep each item in a separate bag, labeled + taped closed

• Collect most fragile evidence first 

  • Fingerprints, bloodstains, trace evidence 

• If unsure – COLLECT IT ANYWAYS or take pictures

Maintaining chain of custody (important part of collecting & packaging evidence)

• Written record to keep track of who has possession of evidence

• This is the state’s record to establish and prove that a particular item of evidence can be positively identified and directly related to the registered offence. It CANNOT be altered, changed.

Final walk through (things that need to happen before the crime scene be released)

• After all evidence is documented, sketched, photographed, and collected, conduct a final walk through to 

  • Verify all evidence has been collected 

  • No equipment is left behind

  • Everything is documented correctly

Crime scene investigation at the scene vs. the lab

• SCENE 

  • Processing, recognized, collected, documented

• LAB

  • Analyzing, identifying, classifying, questioning, reporting