When Science Isn’t So Scientific: How “Elastic” Evidence Can Lead to Wrongful Convictions

One of the subjects that has really intrigued me during my time studying wrongful convictions is the role of expert and scientific evidence. It is often seen as the most objective and trustworthy type of evidence in court, but what I have come to learn is that this is a common misconception. In fact, some forms of scientific evidence can be surprisingly unreliable – and that is something we do not talk about enough.

In this post, I want to explore the idea of evidence elasticity, a concept that helps explain why certain kinds of forensic evidence are more prone to error and bias. As the following will further discuss, this issue plays a major role in wrongful convictions and deserves more attention. 

So, what is evidence elasticity? 

It refers to how much interpretation is involved when experts analyze forensic evidence. The more interpretation required, the more “elastic” the evidence is – and the more vulnerable it becomes to unconscious bias (MacLean et al., 2020). Evidence like DNA tends to be low-elasticity because it follows standardized procedures and leaves little room for subjective opinion. On the other hand, high-elasticity evidence – such as forensic pathology or bloodstain pattern analysis – depends heavily on expert judgment and can vary from one expert to another (Cole, 2012).

This becomes dangerous when expert opinions are shaped by confirmation bias or other external pressures. A well-known example is Dr. Charles Smith, a forensic pathologist who played a key role in several wrongful convictions. In the case of Brenda Waudby, for example, Dr. Smith interpreted inconclusive pathology findings as signs of homicide – largely because he was predisposed to suspect foul play in child deaths (Goudge, 2008). Accordingly, forensic pathology is considered a high-elasticity field because it often involves interpreting complex, ambiguous medical evidence, leaving significant room for subjective judgment. His conclusions were later proven false, but not before they caused significant harm. 

Another striking case is Michael Peterson's conviction, which relied heavily on the testimony of bloodstain pattern analyst Duane Deaver - a case explored extensively in the Netflix documentary 'The Staircase.' Deaver presented his findings in a way that supported the prosecution’s theory, even designing experiments to match their narrative rather than objectively test it. Evidently, bloodstain pattern analysis, a high-elasticity field with limited standardization, allowed Deaver to shape his conclusions around expectations instead of proven evidence. 

So, how do we prevent expert testimony from becoming a tool for bias rather than truth? 

Reforms like linear sequential unmasking have been proposed, which require experts to examine the evidence before being exposed to case details. This helps prevent confirmation bias in cases involving high-elasticity evidence (MacLean et al., 2020). Other important changes include standardizing forensic methods and training forensic professionals to move from a “think dirty” to a “think truth” approach (Goudge, 2008, p. 43). 

At the end of the day, science is not always black and white – especially in a courtroom. The more we understand how elastic evidence works, the better we can recognize its risks and prevent it from leading to the kind of devastating mistakes no one should have to pay for. 

References

Cole, S. A. (2012). Forensic science and wrongful convictions: From exposer to contributor to corrector. New England Law Review, 46(1), 711-736. 

Goudge, S. T. (2008). Inquiry into pediatric forensic pathology in Ontario: Volume 1. Ontario Ministry of the Attorney General. 

MacLean, C. L., Smith, L., & Dror, I. E. (2020). Experts on trial: Unearthing bias in scientific evidence. U.B.C Law Review, 53(1), 101-140.