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Understanding the Role of Forensic Science in Canadian Criminal Trials

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York Regional Police recently solved a 51-year-old cold case of a teenage girl who went missing in Toronto and was later found dead of blunt force trauma to the head in King Township. Using investigative genetic genealogy and crime scene DNA evidence that had been preserved for decades, police investigators identified a Toronto suspect with a known history of violence against women. However, police will not be able to present this forensic evidence at trial to bring the suspect to justice because the suspect died by suicide 19 months after the murder.

The DNA-based forensic science used to identify the suspect is just one out of dozens of distinct forensic science techniques police use to identify criminal suspects and Crown prosecutors rely on as evidence at trial. In fact, forensic evidence often plays a critical role in criminal trials and can be the linchpin that helps determine the guilt or innocence of a suspect. For example, consider that breathalyzer readings used to convict impaired drivers in DUI cases are a form of forensic science.

Given the importance of forensic science evidence, the skilled criminal defence lawyers of the Greater Toronto Area’s Mass Tsang are intimately familiar with the types of forensic science used in police investigations and how the Crown presents this evidence in court. Read on to learn more about forensic science’s key role in Canadian criminal trials.

What is Forensic Science?

Forensic science is perhaps best described as “the application of the methods of the natural and physical sciences to matters of criminal and physical law.” Thus, any scientific field can be forensic when the scientific method is applied to investigating legal matters.

Forensic science has been used to investigate criminal matters since at least the 12th Century, as evidenced by a Chinese book considered the first-ever to use science to investigate suspicious deaths. Washing Away of Wrongs, served as a forensic pathology handbook for coroners by detailing scientific methods to determine causes of death. Translated into multiple languages over the centuries, the book is still in print.

The application of forensic science in criminal matters expanded significantly in the 19th Century. In 1835, Scotland Yard became the first law enforcement agency to trace a bullet back to the fired gun by matching a flaw in the bullet to the original bullet mould. Multiple people from different countries developed the field of dactylography — fingerprint identification — during the century, and by the end of it, major law enforcement agencies had started using it to identify suspects. Other 19th Century initial forensic science breakthroughs include:

  • Hair analysis identification
  • Crime scene photography analysis
  • Body fluid analysis
  • Time of death temperature measurement
  • Physical matching

At the start of the 20th Century, French criminologist Edmond Locard formulated what is now considered the essential principle of forensic science: “Every contact leaves a trace.”

Primary Types of Forensic Science Evidence Used in Court

While any science can be forensic, distinct types have emerged as critical tools to uncover evidence that the Crown can introduce in court. A key factor in using any of them is that the scientific method is rigorously applied to support the validity of the findings.

Today’s police and Crown prosecutors still utilize the forensic science disciplines initially developed in the 19th Century, though scientific advancements have made them even more reliable. Other primary types of forensic science evidence introduced in Canadian criminal trials include:

  • Blood splatter analysis
  • Fibre analysis
  • Chemical analysis
  • DNA analysis
  • Digital analysis
  • Document analysis
  • Forensic archeology (exhumation of buried evidence)
  • Forensic entomology (using bugs to establish the time of death in decomposition cases)
  • Forensic Odontology (identification by teeth and bite mark analysis)
  • Forensic engineering (often reverse engineering to determine elements of car crashes, explosions, and other criminal damages)

Forensic Science Evidence Limitations

Television courtroom dramas often portray forensic science evidence as the deciding factor that puts the bad guys behind bars. However, in the real world, the outcome of most criminal cases depends more on other forms of evidence and witness testimony. More often than not, forensic science plays a supporting role for other evidence introduced in criminal trials. That said, among the forensic science types, fingerprint and DNA-based evidence tend to be the most influential in case outcomes.

When introducing forensic science-based evidence, the onus is on the Crown to prove the evidence is reliable. To do this, prosecutors must:

  • Show how the underlying scientific forensic theory is valid.
  • Demonstrate how the investigatory techniques applied to the forensic theory are valid.
  • Show how the investigatory techniques were properly applied in this particular case.

In response, a skilled criminal defence lawyer can challenge or otherwise raise doubts about the reliability of the forensic science-based evidence. Depending on the type of evidence, a defence lawyer might rely on their own forensic expert to challenge any or all three points the Crown uses to prove evidence reliability. Typical challenges to forensic evidence include:

  • Any studies or research that questions or refutes the validity of the underlying science and/or investigatory techniques used with it.
  • Potential error rates of the applied investigatory techniques used by police.
  • Experience and expertise of the forensic investigator who applied the techniques.
  • Whether evidence was compromised by improper collection or storage methods.
  • Whether any evidence collection tools were properly calibrated.

When faced with forensic evidence, an experienced criminal defence lawyer strives to raise reasonable doubts about its validity. Such reasonable doubts can prove instrumental in securing an acquittal, as the Crown must prove a defendant’s guilt “beyond a reasonable doubt.”

Turn to Toronto’s Mass Tsang for Criminal Defence Expertise

The criminal defence lawyers of Mass Tsang have three decades of experience challenging evidence introduced at trial by Crown lawyers. We’re familiar with the strengths and weaknesses of forensic science evidence presented at trial and know how to challenge it. If you’re facing serious criminal charges in the Greater Toronto Area, turn to us for expert legal guidance and defence. To schedule your free consultation, contact Mass Tsang Today.



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