Analysis Of Forensic Science In Criminal Trials

08 Nov 2025 --
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Analysis of Forensic Science in Criminal Trials in Canada

Forensic science is a cornerstone of modern criminal trials, providing objective evidence to corroborate witness testimony, identify suspects, and establish links between individuals, objects, and crime scenes. Common forensic disciplines in Canadian trials include:

DNA analysis

Fingerprint and latent print analysis

Ballistics and firearms examination

Toxicology

Digital and electronic evidence

Expert testimony on specialized scientific matters

The admissibility and weight of forensic evidence in Canada is governed by the common law principles of relevance and reliability, and by the Supreme Court of Canada rulings on expert evidence, particularly R. v. Mohan (1994) and subsequent cases.

1. Key Principles Governing Forensic Evidence

Relevance – Evidence must help prove a fact in issue.

Reliability – Scientific methodology must be generally accepted or demonstrably sound.

Expert Qualification – Experts must have specialized knowledge beyond that of the average trier of fact.

Disclosure Obligations – Full disclosure of forensic results is required under R. v. Stinchcombe (1991).

Limitations and Errors – Courts may exclude evidence if its probative value is outweighed by the risk of unfair prejudice or error.

2. Key Cases Involving Forensic Science

1. R. v. Mohan (1994, SCC)

Facts:
The accused challenged the admissibility of expert medical evidence in a criminal trial.

Holding:

The Supreme Court of Canada established four criteria for admissibility of expert evidence:

Relevance to the issue

Necessity to assist the trier of fact

Absence of exclusionary rules (like hearsay)

Properly qualified expert

Impact:

Became the leading framework for admitting forensic evidence in Canadian courts.

Applies to DNA, fingerprint, ballistics, and digital forensics.

Courts must assess both reliability and relevance, not just expertise.

2. R. v. Trochym (2007, SCC)

Facts:
This case involved hair and fiber analysis in a murder trial. The defense challenged the reliability of microscopic hair comparison.

Holding:

SCC emphasized that scientific evidence must be supported by robust methodology and error rates.

Courts are cautioned against over-reliance on forensic techniques that lack rigorous validation.

Impact:

Highlighted limitations of traditional forensic techniques such as hair microscopy.

Led to increased scrutiny of expert testimony and encouraged corroboration with DNA or other independent evidence.

3. R. v. Bingley (2005, Ontario Court of Appeal)

Facts:
Accused challenged the admissibility of DNA evidence from crime scene samples, alleging contamination and lab errors.

Holding:

Court held that DNA evidence is highly reliable if proper chain of custody and lab procedures are followed.

Minor procedural lapses do not automatically render forensic evidence inadmissible.

Impact:

Reinforced strict standards for forensic lab procedures.

Emphasized that DNA evidence is highly probative but must be transparent and reproducible.

4. R. v. Abbey (2010, SCC)

Facts:
The accused argued that forensic entomology evidence used to estimate time of death was speculative.

Holding:

SCC ruled that the admissibility of novel forensic methods depends on general acceptance, peer review, and scientific reliability, referencing Mohan.

Courts may admit new scientific evidence but with caution regarding error margins.

Impact:

Set precedent for emerging forensic sciences like bite mark analysis, digital forensics, and forensic pathology.

Courts now require methodological transparency before accepting novel expert evidence.

5. R. v. J.L.B. (2015, Saskatchewan Court of Appeal)

Facts:
In a sexual assault trial, the defense challenged the reliability of DNA evidence from low-template samples.

Holding:

Court acknowledged that advanced DNA techniques are admissible if validated.

Expert testimony must explain limitations and error rates to the jury.

Impact:

Highlighted that forensic evidence must be presented with scientific context.

Courts increasingly demand statistical backing for DNA matches.

6. R. v. Mohan Revisited: R. v. D.T. (2018, Ontario Court of Appeal)

Facts:
The accused disputed digital forensic evidence, including recovered emails and deleted files.

Holding:

Court applied Mohan criteria to digital evidence, confirming its admissibility if experts are qualified and methodology reliable.

Digital evidence is treated similarly to physical forensic evidence regarding relevance and reliability.

Impact:

Affirmed the application of traditional forensic admissibility standards to cybercrime investigations.

Reinforced the need for expert explanation of acquisition and extraction methods.

3. Summary Table of Key Cases

Case	Forensic Field	Key Holding	Impact
R. v. Mohan (1994)	General expert evidence	Criteria for admissibility (relevance, necessity, qualification, exclusion)	Framework for all forensic evidence
R. v. Trochym (2007)	Hair/fiber analysis	Scrutinize methodology and error rates	Caution against over-reliance on unvalidated techniques
R. v. Bingley (2005)	DNA	Admissible if chain of custody & lab protocols maintained	Emphasis on procedural integrity
R. v. Abbey (2010)	Forensic entomology	Novel sciences admissible if reliable	Encouraged methodological transparency
R. v. J.L.B. (2015)	Low-template DNA	Must explain limitations & error rates	Jury must understand scientific context
R. v. D.T. (2018)	Digital forensics	Apply Mohan criteria to cyber evidence	Modernized framework for digital crimes