Detailed Evidence Processing Techniques
This section delves deeper into the specific techniques used for processing different types of physical evidence, emphasizing the importance of proper handling and analysis.
Bodily Fluids and Tissues
DNA extraction from bodily fluids and tissues is a critical aspect of many criminal investigations. The process involves:
- Careful collection using sterile swabs or by cutting out stained fabric
- Air-drying wet samples to prevent degradation
- Packaging in paper bags to allow air circulation and prevent mold growth
- Sealing and labeling each item separately to maintain chain of custody
- Rapid transfer to a forensic laboratory for analysis
Example: In sexual assault cases, victims should be examined by a doctor or police surgeon as soon as possible to collect DNA evidence.
Fingerprint Analysis
Fingerprints are processed using various methods depending on their type:
- Latent prints: Made visible with powders or chemical treatments, then photographed and lifted with adhesive tape
- Patent prints: Visible prints in substances like blood or ink are photographed directly
- Plastic prints: Three-dimensional impressions in soft materials are photographed and cast
Highlight: Collected fingerprints are compared to the IDENT1 database, which contains prints of all arrested individuals, to identify potential matches.
Impression Evidence
This category includes various types of marks left at crime scenes:
- Bite marks: Examined, swabbed, and photographed by a police surgeon; sometimes cast for analysis by a forensic odontologist
- Shoeprints: Photographed, cast if in soil, and compared to the National Footwear Reference Collection
- Tire marks: Analyzed for unique characteristics developed by wear patterns
Trace Evidence
Trace evidence encompasses a wide range of small-scale materials:
- Fibers: Collected using tweezers, wrapped in paper, and sealed for laboratory analysis
- Paint flakes: Carefully collected and analyzed to identify specific types and manufacturers
- Soil samples: Collected from various locations for comparison and analysis
- Gunshot residue: Collected from suspects' hands or clothing for chemical analysis
Vocabulary: Toxicology is the study of poisons, drugs, and alcohol in the body, often used in criminal investigations to determine substance use or poisoning.
The processing of physical evidence requires meticulous attention to detail and adherence to strict protocols. Each step, from collection to analysis, plays a crucial role in maintaining the integrity of the evidence and ensuring its admissibility in court. The collaboration between crime scene investigators, forensic scientists, and specialized experts is essential for the successful processing and interpretation of physical evidence in criminal investigations.
