This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: CSI may have spawned innumerable spinoffs, but it turns out you can't trust TV—or sniffer dogs. New research is questioning the scientific basis for the dogs' use by police, as well as aspects of bloodstain pattern analysis and ballistics evidence routinely used in courts.
One published paper in The Alberta Law Review and two forthcoming articles in The Canadian Bar Review and The Dalhousie Law Journal examine how courts treat these forms of evidence and argue that greater scrutiny is needed. "Just because a technique has been used in court for decades doesn't mean we should take its reliability for granted, especially when someone's liberty is at stake in a criminal trial," said author Sara Gordon, associate professor at the Peter A. Allard School of Law at UBC.
"My hope is that this research will help judges and lawyers better understand the limitations of these techniques and ensure that forensic evidence is presented in a way that accurately reflects what the science can—and can't—tell us." Gordon noticed a lag between advances in the scientific understanding of forensic evidence and its treatment in court. She examined several forensic and investigative techniques commonly used by police and regularly admitted as evidence in North American courts—some of which have played an important role in securing convictions—and found significant gaps in the scientific support. Ballistics evidence is perhaps the most familiar: Bullets and cartridge cases are matched to a particular firearm.
While ballistics evidence has been accepted in Canada for more than a century, Gordon found that scientific research does not support the level of confidence with which ballistics experts often testify. In practical testing, for example, examiners misidentified bullets 37% of the time. Gordon's forensic firearms article focuses on the use of this evidence in Canada, where it continues to be routinely admitted.
In 2023, however, a Chicago court became the first in the United States to bar the use of ballistics-matching evidence in a criminal case. In Canada, police may use a drug-detection or "sniffer" dog to conduct a search when they have reasonable suspicion that the search will reveal evidence of a drug offense—a lower threshold than ordinarily required for a warrantless search. The Supreme Court of Canada has justified this on the basis that sniffer-dog searches are minimally intrusive, narrowly targeted and highly accurate.
But Gordon's review of the scientific evidence that has emerged since the court's latest rulings in 2013 indicates otherwise. "They're not nearly as reliable as many courts seem to assume. And in fact, they can be quite invasive." The accuracy of sniffer dogs has been called into question repeatedly around the world.
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