Collection of Evidence
Forensic Evidence: Types and Collection Techniques
Overview
Forensic evidence plays a critical role in crime scene investigations. Proper handling and collection techniques are essential to ensure the integrity of the evidence.
Types of Evidence Collected from Crime Scenes
Hair Evidence
Fiber Evidence
Paint Evidence
Drug Evidence
Arson Evidence
Explosive Evidence
Rape Evidence
Biological Evidence
Firearms Evidence
Toolmarks Evidence
Other Impression Evidence
Handwriting Evidence
Fingerprints Evidence
Collection Techniques
Hair Evidence
Questioned and control hairs must come from the same body area.
Collect hair by pulling or clipping close to the skin; scalp hairs and a minimum of two dozen pubic hairs are needed.
In sexual assault cases, a clean comb is used for collection, with careful packaging of all samples.
Samples must be collected during the autopsy to avoid legal issues.
Fiber Evidence
Requires significant training for proper identification and preservation.
Articles of clothing must be placed in separate paper bags to avoid contamination.
Fragile materials, such as carpets and bedding, should be handled carefully, with car seats covered in polyethylene sheets.
Adhesive tape lifts from the victim can reveal fiber evidence.
Paint Evidence
Loose paint chips should be meticulously collected to maintain integrity.
Use tweezers or paper to collect paint chips, submitting the entire item if paint is embedded.
Control samples should come from undamaged areas of suspected items for comparison.
Care needed when recovering tools with paint traces; package and label properly.
Drug Evidence
Drugs must be properly packaged and labeled to prevent contamination.
Volatile substances should be contained in airtight packages.
Background information on drugs assists analysts in their evaluation.
Arson Evidence
Collect soot and ash debris from the fire's origin in airtight containers.
Substrate controls help differentiate accelerants.
Other important items: ignitors, firearms, and the suspect's clothing.
Accelerants in soil should be frozen to prevent microbial degradation.
Explosive Evidence
Samples collected post thorough search; include materials from the blast origin.
Soil and debris should be separated into appropriate containers.
Use the EGIS system in lab for residue screening.
Rape Evidence
Semen is critical but absence does not negate the possibility of rape.
Other evidence includes injuries and transferred samples from contact.
Package clothing and evidence separately to avoid contamination.
Biological Evidence
Photograph biological material at crime scenes and document locations.
Wear gloves, change frequently, and avoid direct contact.
Package all clothing, something stained, separately in ventilated containers.
Collection of Firearms Evidence
Pick up weapons carefully to avoid disruption of evidence; prioritize safety.
Document conditions and location of all ammunition before unloading.
Label all evidence for identification and maintain the chain of custody.
Do not dry or clean weapons recovered from water before sending to the lab.
Ammunition Evidence
Protect markings on bullets and cartridge cases by careful handling.
Identify bullets with initials and package to avoid damage.
Document and compare ejection patterns when multiple rounds are fired.
Tool Marks Evidence
Tool marks are created when tools contact other objects; consider class and individual characteristics.
Preserve the object or take a cast of the impression when possible.
Handle tools and marks with care to avoid evidence loss.
Other Impressions
Impressions from shoes, tires, or fabric must be documented and preserved.
Photograph impressions with scales before handling.
Cast soft impressions, avoiding cleans that might compromise the evidence.
Handwriting Examples
Collect known writings that mirror the questioned document.
Gather multiple samples to show variations in the suspect’s writing.
Look for age discrepancies between documents to establish authenticity.
Exercises
Discuss potential issues that could compromise the collection of:
Fiber Evidence
Drug Evidence
Arson Evidence
Biological Evidence
Firearms Evidence