Use Of Forensic Evidence In Canadian Trials
1. DNA Evidence
Definition & Importance:
DNA (Deoxyribonucleic Acid) evidence is genetic material that is unique to each individual (except identical twins). DNA can be extracted from blood, hair, saliva, semen, skin, or other bodily tissues. It is used to identify or exclude suspects, link crimes, and sometimes establish familial relationships.
Reliability:
DNA evidence is highly reliable because it is unique to an individual. However, proper collection, preservation, and laboratory analysis are critical to avoid contamination.
Key Cases Involving DNA Evidence
Case 1: People v. Castro (1989, New York)
Facts: Castro was accused of sexual assault. The prosecution introduced DNA evidence matching Castro to the crime scene.
Legal Issue: Whether DNA evidence could be admitted without first establishing scientific reliability and proper methodology.
Decision: The court stressed that DNA evidence must meet scientific reliability standards, and juries must understand its limitations.
Impact: Established rigorous standards for introducing DNA evidence in court and influenced the Frye standard for scientific evidence.
Case 2: R v. Doheny (1997, UK)
Facts: Doheny was accused of murder, and DNA evidence linked him to the crime scene.
Legal Issue: Whether DNA statistical probabilities could be presented to the jury.
Decision: The court ruled DNA evidence admissible but cautioned that statistical probabilities should not mislead jurors.
Impact: Emphasized careful explanation of DNA statistics to prevent misunderstanding by juries.
Case 3: People v. Wesley (1990, California)
Facts: Wesley was charged with murder. Semen found at the crime scene was tested for DNA.
Legal Issue: Reliability of DNA testing methods used by laboratories.
Decision: DNA evidence was admitted after experts testified on techniques and controls used.
Impact: Highlighted the importance of lab procedures and expert testimony to ensure DNA evidence is credible.
Case 4: State v. Michaels (2000, Ohio)
Facts: Michaels was accused of sexual assault. DNA from a swab matched the defendant.
Legal Issue: Defense argued contamination and mislabeling of samples.
Decision: Court ruled DNA evidence admissible because chain of custody and lab documentation were intact.
Impact: Reinforced the importance of chain of custody in handling DNA samples.
2. Fingerprint Evidence
Definition & Importance:
Fingerprint evidence is based on the uniqueness of friction ridge patterns on human fingers. Fingerprints can be found on objects, doors, or surfaces touched by a person.
Reliability:
Fingerprint identification has been widely accepted for over a century. Each print is considered unique, and methods such as AFIS (Automated Fingerprint Identification System) increase accuracy.
Key Cases Involving Fingerprint Evidence
Case 1: People v. Jennings (1987, New York)
Facts: Fingerprints found at a robbery scene were linked to Jennings.
Legal Issue: Defense challenged the fingerprint expert’s methods.
Decision: Court admitted the fingerprint evidence, recognizing it as a scientifically accepted method of identification.
Impact: Confirmed fingerprints as reliable evidence in criminal cases.
Case 2: United States v. Mitchell (1999, Federal Court)
Facts: Mitchell was accused of burglary. Latent prints matched Mitchell’s fingerprints.
Legal Issue: Defense questioned expert qualifications and methodology.
Decision: Court admitted evidence because the expert had proper credentials and followed standard procedures.
Impact: Emphasized expert qualifications and proper methodology in fingerprint analysis.
Case 3: R v. Doheny & Adams (UK, 1997)
Facts: This case also involved fingerprint and DNA evidence. Fingerprints matched the defendants.
Legal Issue: Whether fingerprint comparison is sufficiently reliable.
Decision: Court recognized fingerprints as admissible, but highlighted the need for expert explanation to the jury.
Impact: Reinforced combined use of DNA and fingerprint evidence.
Case 4: State v. Timmreck (1997, Wisconsin)
Facts: Fingerprints on stolen property matched Timmreck.
Legal Issue: Accuracy of latent fingerprint matching.
Decision: Evidence admitted; expert testimony clarified matching process and probability of error.
Impact: Demonstrated the importance of explaining limitations and error rates in fingerprint evidence.
Case 5: People v. Hill (2000, California)
Facts: Hill accused of homicide; fingerprints found at scene.
Legal Issue: Whether fingerprint evidence alone is sufficient for conviction.
Decision: Fingerprint evidence was admissible and persuasive, but court noted jury should consider all evidence.
Impact: Fingerprints are strong but should be corroborated with other evidence when possible.
3. Key Takeaways
DNA Evidence: Highly reliable but requires strict lab protocols, chain of custody, and careful statistical interpretation.
Fingerprint Evidence: Long-established method, unique to each individual, but requires expert testimony and explanation to prevent misunderstanding.
Case Law Lessons: Courts emphasize scientific reliability, expert qualifications, chain of custody, and careful explanation to juries.
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