Physical Evidence Techniques

Understanding Physical Evidence

Physical Evidence refers to materials or objects present at a crime scene that can help to establish facts or connections in a crime. These can include fingerprints, tyre marks, footprints, tool marks, gun residue, and more.
The key aspect of physical evidence is that it is tangible, meaning it can be seen, touched, and measured.
Physical evidence can help reconstruct a crime scene, identify a suspect or victim, or even establish the sequence of events.

Before any collection takes place, the crime scene and evidence should be thoroughly documented. This includes photography, sketching, and written notes of the scene and the evidence within it.

Silicone-based putties or fingerprint powders can be used to lift fingerprints off surfaces.
Collected fingerprints should be placed on clear tape, then attached to a contrasting colour card for analysis.

Special adhesive tapes or vacuum devices can be used for collecting trace evidence such as fiber, paint chips, or glass fragments.
Individual and mass samples should be collected - individual samples are trace evidence that can be picked up and packaged separately while mass samples involve collecting larger items or areas that may contain trace evidence.
Collection personnel should avoid cross-contamination, which can mislead the investigation process.

Silicone or dental stone casting can help to record and preserve the impressions of footwear and tyre marks.
Two-dimensional marks can be lifted with electrostatic lifters or gelatin lifters.

Bullet casings, shells, and fragments, as well as tool marks, can be collected and preserved for further analysis. Care should be taken not to damage the unique tool marks on these items.

Pack all collected evidence separately in suitable containers to prevent cross-contamination, degradation or loss of trace evidence.
Use secure, tamper-evident packaging for all physical evidence for maintaining the chain of custody.
Labels on each evidence package should clearly indicate the case number, item number, exact location of collection, date, and the initials or signature of the collector.
Store collected evidence in a secure environment until it is ready for analysis. Certain types of evidence may require refrigeration or other specific storage conditions.

Accuracy in collection, preservation, and analysis of physical evidence is key in forensic investigations.
Using the proper tools and techniques, and adhering to established procedures helps maintain evidence integrity and ensures its admissibility in a court of law.