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.

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.

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.

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.