Biological Evidence Techniques

Biological Evidence Techniques

Collection of Biological Evidence

  • Biological evidence constitutes material items at the crime scene that are biological in nature, such as blood, hair, saliva, semen or body tissues.
  • Examiners must bear in mind the types of biological evidence that might be present at a crime scene, which can often be invisible to the naked eye.
  • Professionals must always use personal protective equipment (PPE) during the collection process to protect themselves and avoid contamination of the evidence.
  • Sterile, single-use collection tools are important to avoid cross-contamination between evidence.
  • Proper packaging is essential to prevent degradation of biological evidence during storage and transport.

Analysis of Biological Evidence

  • Biological evidence is often sent to a forensic laboratory for further detailed examination.
  • Techniques such as microscopic examination can be used to identify hairs or fibres.
  • Prior to any DNA analysis, biological evidence must be screened for the presence of sufficient cellular material.
  • DNA extraction is performed to isolate DNA from the cells present in the evidence sample.
  • DNA profiling (also known as DNA fingerprinting) generates a unique pattern for each individual, which can be compared with reference samples.
  • Other types of forensic analysis for biological evidence include bloodstain pattern analysis, serology (study of blood serum), and toxicology.

Interpretation of Biological Evidence

  • Forensic scientists must provide a professional interpretation of the results of the analysis, linking the biological evidence to a potential suspect or ruling out individuals.
  • Statistical analysis is often performed to determine the likelihood that the DNA profile would occur by chance in the population.
  • Biological evidence can be significant in supporting or rejecting alibis or suspect statements.
  • It is key to provide a clear, fact-based report of the findings, which can be used in court to support legal proceedings.

Preservation and Continuity of Biological Evidence

  • Preserving the integrity of biological evidence from the crime scene to the courtroom is crucial.
  • All handling and transfer of evidence should be meticulously documented in a chain of custody.
  • Storage conditions, such as temperature, humidity and light levels, should be controlled to prevent degradation.
  • Proper preservation of biological evidence can help ensure it is admissible in court and can provide irrefutable links between suspects, victims and crime scenes.