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Evidence Handling Procedures William J. Tilstone and John H.…
Evidence Handling Procedures William J. Tilstone and John H. Dillon Jr. “Module 06: Evidence Handling Procedures.” Firearm Examiner Training, National Forensic Science Technology Center, projects.nfstc.org/firearms/module06/fir_m06.htm.
Types of Evidence
Biological
Examples: blood, semen, saliva, bone, hair, skin
Integrity can be compromised by degradation and contamination
Safety precautions when working with biological evidence: wear personal protective equipment, don't eat around it, and dispose of the evidence safely
Touch DNA from triggers, hammers, grips, etc.
Drug
Can range from simple powders to manufacturing laboratories
Physical
Examples: firearms evidence, fingerprints, toolmarks, impressions, trace evidence
Corroborative and/or circumstantial evidence
Trace Evidence
Examples: hair, fibers, glass, paint
Other
Measurements taken of distances and angles on the crime scene
Questioned documents
Toxicology
Data files on computers
Laboratory Evidence Handling
Integrity: labs have strict procedures to preserve integrity
Chain of Custody: complete chain of custody must be kept
Safety:loaded firearms, biohazards, sharp tools
The Crime Scene
Location of Evidence: spiral, parallel, grid, zones, with the naked eye, equipment, or laboratory testing
Collection of Evidence
Firearms evidence: firearm, ammunition, gunshot residue, etc.
Fired bullets: package separately to prevent additional marks from being made upon them
Fired cartridge cases and shotshells: also package separately for the same reason
Related evidence: things with bullet holes
Toolmark evidence: tools must be preserved and packaged separately in a strong container
Toolmarked items
Chain of Custody
Preservation and Packaging: plastic containers used usually- but NOT for biological evidence
Recording the Scene: notes, diagrams, and photography
Firearms and Fired Ammunition Components
Protecting the Scene: restricting access and wearing PPE reduces contamination and loss of evidence
Unfired Ammunition: hand-carried to laboratory because it is potentially dangerous
Firearm and Toolmark Examination Considerations
Latent Prints: can be found on used firearms
Gunshot Residue: can sometimes be seen with the naked eye but other times need color changing tests or microscopy to view
Trace Evidence: bone fragments and hair on fired bullets
Metal Smears: can be seen under a microscope
Biological: can be found on knives, muzzles of firearms, and on the actual fired bullet
Associative evidence
Examples: latent prints, fibers, blood, semen, saliva, hair, paint, glass, soil, and impressions
Value depends on:
Frequency: frequency of DNA composition at the thirteen core loci
Persistence: some evidence sticks around for a while (fingerprints and biological evidence), but some falls off easily (hair and fibers)
Specificity: DNA is very specific, but fragments of glass aren't always
Alternate Explanations: consensual sex vs. rape (semen) or giving assistance vs. harming someone (blood)
Evidence Submission: letter of transmittal
Documentation: case number, location of crime, date of crime, photographs, summary of crime, chain of custody, etc.
Receipt of Evidence: usually given to reception personnel
Case Tracking Within Laboratory
Storage Options: centralized or decentralized systems
Physical Integrity of Evidence: kept through environmental controls, alarm systems, video cameras, refrigeration, and fume hoods
Evidence Distribution
Centralized System: Laboratory manager breaks seal and distributes evidence to examiners
Examiner-based System: Examiner breaks seal and acts as hub of chain of custody while in lab
Controlled Access: layered security
Case Assignment
High Security: some pieces of evidence are kept in separate storage facilities with very restricted access
Forensic LIMS
Input Information: case number, chain of custody, bar code, estimated date of completion, ect.
Output Information: information about status and progression of a case