Perpetuating the Presumption of Guilt: The Role of Implicit Racial Bias in Forensic Testimony

Criminal Law Bulletin, forthcoming volume 58 (2022)

36 Pages Posted: 21 Aug 2021

See all articles by Aliza B. Kaplan

Aliza B. Kaplan

Lewis & Clark Law School

Janis Puracal

Forensic Justice Project

Date Written: August 19, 2021


Since the murders of George Floyd and Breonna Taylor, conversations around racial bias in the criminal justice system have accelerated. Much of the focus has turned to police reform. The potential for racial bias, however, does not end with the initial stop, search, and arrest. Rather, it can be found throughout our criminal justice system, and forensic testimony is one area that does not get nearly enough attention when it comes to implicit racial bias.
Lawyers, judges, and jurors often approach scientific sounding evidence with a predisposition to accept the expert’s conclusions, without a critical eye. Experts for the government are often presumed to be neutral and objective witnesses who report the science with no stake in the outcome.

Government experts, however, are susceptible to bias, including implicit racial bias, just like the rest of us. These experts who testify in criminal cases may not be reporting “neutral science”; the testimony may be contaminated by implicit racial bias, among other biases, that has colored their conclusions.

Pattern matching methods —for example, analysis of firearms and toolmark impressions, bloodstains, latent prints, hairs, and footwear and tire impressions—are especially problematic. These methods are inherently subjective, meaning that they rely heavily on the examiner’s individual judgment, rather than any objective standard. Even though the examiner may be analyzing, for example, a bullet from a crime scene, that examiner may also be given “irrelevant contextual information,” such as the name, race, and background of the lead suspect. Knowing that information can predispose the examiner to believe that the bullet was fired from that suspect’s gun, leading to a result-driven opinion about whether the marks on the bullet “match” the marks on test fires from the gun. The human eye will see what it wants to see, and, because there are no objective standards by which to measure the marks, the examiner’s conclusions may reflect bias in favor of guilt, rather than a true determination that the marks are, in fact, the same in appearance or sufficient in number. For many law enforcement-led forensic labs, that predisposition toward guilt exists regardless of knowledge about the suspect’s race; knowing that information only adds to the level of bias—a bias that is often difficult to identify because it is unspoken and rooted in decades of societal learning that has created presumptions about dangerousness, culpability, and propensity toward violence based on race.

A number of recent exonerations have raised questions about the role of implicit racial bias in faulty forensic testimony that resulted in a wrongful conviction. For example, there are cases in which an examiner’s opinion changed over time from inculpatory to exculpatory or neutral. The million-dollar question is what led the examiner to the inculpatory opinion in the first place, especially when that opinion ultimately proves to be changeable without any new information about the evidence itself.

In this article, we address how implicit racial bias can affect forensic testimony and ways to address it before wrongful convictions occur. In section II, we explain what implicit bias is. In section III and IV, we discuss the presumption of guilt that exists in our criminal justice system for people of color especially Black and Brown people. Section V provides an overview of the relative lack of attention that implicit racial bias has received in forensic reform to date. In section VII, we examine how widespread acceptance of forensic evidence as objective and impartial ignores how implicit racial biases in forensic testimony perpetuate the presumption of guilt for people of color in our criminal justice system. In sections VIII and IX, we indicate the steps necessary to limit implicit racial bias and provide examples of what can be done to address it in forensic testimony such as auditing state forensic labs, creating independent (not law enforcement led) forensic labs, conducting root cause analyses in forensic labs, and cross-examining the government’s forensic experts about how implicit racial bias may have infected their opinions. Finally, we conclude in section X that, in order to fully address the impact of implicit racial bias in the criminal justice system, we must acknowledge and address the role that forensic testimony plays in perpetuating the presumption of guilt for people of color.

Keywords: criminal law, forensic, race

JEL Classification: K14

Suggested Citation

Kaplan, Aliza B. and Puracal, Janis, Perpetuating the Presumption of Guilt: The Role of Implicit Racial Bias in Forensic Testimony (August 19, 2021). Criminal Law Bulletin, forthcoming volume 58 (2022), Available at SSRN:

Aliza B. Kaplan (Contact Author)

Lewis & Clark Law School ( email )

10015 S.W. Terwilliger Blvd.
Portland, OR 97219
United States

Janis Puracal

Forensic Justice Project ( email )

333 S.W. Taylor St.
Suite 400
Portland, OR 97204
United States
503-664-3641 (Phone)


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