How WA Police Use Forensic Science To Investigate Crimes

Forensic science plays a pivotal role in criminal investigations undertaken in Western Australia. By employing advanced scientific techniques, forensic specialists assist detectives in gathering and interpreting evidence to reconstruct crime scenes and identify suspects.

This article outlines the key forensic disciplines used in WA, including crime scene analysis, forensic pathology, fingerprint identification, trace evidence analysis and forensic DNA profiling.

Crime Scene Examination

The first step in a forensic investigation is securing and examining the crime scene. Key elements of crime scene investigation include:

• Photographic documents: where scenes are recorded using high-resolution photography, videography, and sketches to capture evidence in situ.
• Evidence collection: where examiners gather physical evidence such as fingerprints, footprints, weapons, and trace materials like hair, fibres and paint.
• Latent evidence identification: which involves the identification of substances like blood, semen, or gunshot residue, which are not immediately visible, through various visualisation techniques.

‘Crime scene reconstruction’ refers to the process of determining what happened at a crime scene using deductive and inductive reasoning. As part of this process, investigators may assess bloodstain patterns at a scene to determine type and direction of impact, as well as analysing footprints, drag marks and displaced objects to determine movement in a scene.

Forensic Pathology

Forensic pathologists, who are medical professionals, will often assist investigators in WA to determine the cause and manner of death in homicide cases. The process of determining cause and manner of death is called the ‘forensic autopsy’.

The forensic autopsy is a systematic examination of a body to determine the cause of death. It consists of a preliminary, external, and internal examination.

The preliminary examination involves visually inspecting the body, collecting personal and medical information, and obtaining biological samples such as blood, urine, and saliva. Advanced identification techniques, including fingerprinting, DNA profiling, and dental record comparison, may be used, particularly when decomposition or injury complicates identification.

The external examination focuses on wound analysis, classifying injuries into bruises, abrasions, incised wounds, and lacerations, while also identifying specific forensic markers such as gunshot residue or petechiae, which can indicate strangulation.

The internal examination involves opening the body with a Y-incision to inspect organs for signs of disease, injury, or poisoning. For instance, toxic substances in the stomach or intestines may suggest poisoning, while water congestion in the lungs could indicate drowning. Histopathology, or microscopic examination of tissues, further refines findings. After the autopsy, the body is reconstructed and returned to the next of kin.

Fingerprint Identification

Fingerprint identification or ‘fingerprint comparison’ is premised on the idea that no two individuals have identical fingerprints, with friction ridge characteristics (minutiae) on each individual’s fingerprint forming the basis of comparisons.

Fingerprint comparison in WA follows the ACE-V method, standing for ‘Analysis, Comparison, Evaluation, and Verification. Friction ridge patterns on a fingerprint are first categorised into loops, whorls, and arches, each with unique variations. These prints are then compared for similarity, evaluated for consistency and then peer-reviewed for verification.

If no suspect print is available, crime scene prints can be searched against the National Automated Fingerprint Identification System (NAFIS), allowing police to rapidly match prints with existing records.

Trace Evidence Analysis

‘Trace evidence’ refers to any type of evidence occurring in sizes so small that it can be transferred or exchanged between two surfaces without being noticed. Examples of trace evidence include:

• Hair (human or animal)
• Skin cells
• Saliva, semen or blood
• Clothing or carpet fibres
• Paint chips or flakes
• Broken glass
• Soil, sand or pollen
• Gunshot or explosive residue

Trace evidence can be examined via a comparison microscope to note similarities that potentially link a suspect to a scene. More complex chemical analysis (for example, gas chromatograph mass spectrometry) may be able to note similarities at the molecular level.

Forensic DNA Profiling

Forensic DNA profiling is the process of extracting, amplifying, and analysing specific regions of an individual's DNA to create a unique genetic profile that can be compared to crime scene evidence, suspects, or databases.

This technique relies on short tandem repeat (STR) analysis, which examines highly variable sections of DNA, allowing forensic scientists to establish identity, exclude individuals, or determine biological relationships with high accuracy.

DNA can be sourced from biological material such as blood, saliva, and hair, and is extracted through methods that break down cell walls to release genetic material. A unique genetical profile can be analysed to determine chromosomal sex as well as compared against known samples or the National Criminal Investigation DNA Database to identify potential matches.

Potential Forensic Errors

While forensic science is a powerful investigative tool, it is not without flaws. Errors in forensic analysis, misinterpretation of results or reliance on discredited techniques can contribute to wrongful convictions. Further, issues such as cross-contamination, sample degradation, cognitive bias and overstated expert testimony have all been identified as risks within forensic investigations.

Notably, high-profile cases such as the wrongful conviction of Lindy Chamberlain, where flawed forensic evidence was central to the prosecution’s case, highlight the potential consequences of forensic errors.

To mitigate these risks, forensic laboratories in Western Australia follow strict accreditation standards and quality control procedures, including proficiency testing and peer review of results. Additionally, legal safeguards such as the requirement for forensic evidence to meet the admissibility standards under the Evidence Act 1906 (WA) and scrutiny under cross-examination aim to ensure the reliability of forensic findings.

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PLEASE NOTE: The material in this blog post is for informational use only and should not be construed as legal advice. For answers to your questions regarding this or other topics, please contact a professional legal representative.