Understanding Crime Scene Investigation and Forensic Evidence
The process of crime scene investigation involves meticulous collection and analysis of physical evidence. Criminology unit 3 case studies demonstrate how forensic specialists and crime scene investigators work together to gather crucial evidence. When processing a crime scene, investigators must follow strict protocols for evidence collection and preservation.
Physical evidence includes bodily fluids like blood and semen, which must be allowed to air dry before being packaged in paper bags and then sealed in polythene bags. Each piece of evidence requires individual packaging and proper labeling. For sexual assault cases, victims undergo examination by police surgeons who collect swab samples. Hair samples can help match suspects to crime scenes and must be carefully wrapped in paper bags, sealed, and labeled.
Definition: Locard's Exchange Principle states that when two objects come into contact, there is always a transfer of material between them. This foundational principle of forensic science explains why trace evidence is so important.
Fingerprint evidence comes in three main forms: patent (visible), latent (invisible), and plastic (indented). Investigators use specialized techniques like dusting with magnesium powder and UV light to reveal latent prints. Other important physical evidence includes shoe prints, which can be photographed and cast if found in soil, and trace evidence like fibers that require collection with tweezers and proper packaging to prevent contamination.







