crime scene processing

Four roles/tasks of documenting the scene and the evidence

6 types of evidence

• testimonial, behavioral, physical, biological(& chemical), trace, medical(& digital)

  • testimonial example: statement from eye-witness, victim, or suspect

  • behavioral example: suspect criminal actions inferred from physical evidence

  • physical example: any & all relevant materials/objects associated w/ crime scene, victim, suspect or witness

  • biological/chemical example: blood, semen, or drugs

  • trace example: fiber, hair, glass, paint, & soil

  • medical/digital example: wounds or electronic device

4 types of conclusions on evidence examination

• Exclusive also known as eliminated

• Link/Association: person of interest because of relationship

• Inclusive/Identification: identifying person who committed crime

• Inconclusive: cannot make decision due to lack of evidence or technology

Locard’s Exchange Principle: when 2 objects come into contact, materials are exchanged between them

Three “Eaches” in COC (chain of custody)

• each person writes down in chronological order of who was responsible of evidence

• each piece of evidence from scene to courtroom

• each consumption by examination (used)

Close Ups vs Mid Range vs Overall View in Photography

• close up pic shows details, specific features of impression/evidence

• midrange pic shows body or tool used in crime scene

• overall pic shows everything in a bird pov

• photographer must have reference(window, door, street sign)

Triangular vs Baseline vs Polar Coordination (measurements)

• all these sketch techniques need 2 fixed points (ex: pole, window)

Zone vs Line vs Grid vs Strip Search Pattern

• spiral, grid & strip/ine is used for outdoor crime scene

• systematic search methods: all of above + quadrant zone

• spiral systematic search has no boundary(start inside and go out)

• indoor crime scene is quadrant zone so each investigator is in charge of one zone or else scene gets contaminated

Rough/Raw vs Final Sketch

• raw sketch includes measurements

• final sketch is usually made by computer in 3D form

Unknown vs Known vs Substrate Control Samples

• unknown sample is questioned at the scene

  • needs evidential value: class, subclass, individual

  • degree of proof: associate, link, identify

• known sample: exemplar from a known source (suspect or victim)

  • such as blood, glass, paint, hair, fiber

  • has to come from the same source for comparison

• substrate control sample: next to the unknown sample or also known as reference sample

False Positive vs False Negative Errors

• false positive is a type 1 error

  • example: put wrong person in prison

• false negative is a type 2 error

  • example: did not capture the correct criminal

Positive vs Negative Control Tests

• positive control: using real blood or drugs we know it has to come out positive

• negative control: using a pen because we know it will come out negative

Search vs Arrest Warrants

• search warrants: legal court issued by judge based on probable cause

  • need to have 51% certainty, physical evidence, & must specify time/location/object

  • affidavit is legal term for search warrant application

• arrest warrants: legal court order issued by supreme court & 4th amendment

Open Field vs Plain View Doctrine

• plain view: only things you can see in public places(ex: restaurant/street) are things police can confiscate & use as evidence

• open field: forest/grassland

Emergency/Exigent Situation vs “Murder Scene Exception”

• this is an exception to the 4th amendment

  • you may stop and frisk a person (use back of hands not palms!!)

  • vehicle inventories

  • another exception:

    • border searches (amendment doesn’t cover border line)

    • consent search: you allowed police to search therefore search warrant is waived

  • reasonable suspicion has to be around 20% certainty (there has to be suspicious behavior or verbal statements)

  • beyond reasonable doubt is 95% - ready to convict

  • if a murder happened you may go into crime w/o warrant but don’t collect evidence because for that you need a warrant

  • search incident to lawful arrest: if officer saw physical evidence they may stop suspect and search them on top of car therefore you can automatically the vehicle becomes part of search incident so you can search it too

Types of Evidence Containers

• handbag: to preserve possible dna sample in fingernails

• waxpaper: for oily evidence

• aluminum can: for metal objects/sharp objects

• foil lined wrapper bag: for electronic/digital evidence

• plastic bags

• regular paper bags

Types of Crime Protection

• nylon gloves

• nitrile

• latex

• polyester

• cotton

• note! leather gloves shrink when blood soaked

• shower cap for shoes & head

Key Points from Video

• in crime lab latex gloves are used frequently

• in crime scene nitrile gloves are used the most

• results of evidence in lab take 4-12 hrs or even 24 hrs depending on complexity of the evidence

• collecting fingerprint method: dusting or w/tape

  • if you dust it you risk removing dead skin cells so ultimately it depends how good the fingerprint is