The CSI Effect

By Robert A. Perry

On July 7 the Las Vegas Metropolitan Police Department issued a video that explained how a mix-up in the department’s crime lab led to the conviction and imprisonment of an innocent man.[1]

The video presentation provided a detailed, step-by-step replay of what was essentially a documentary exposé of the manner in which apparently mundane human error can confound the science of forensic DNA-a technology that is perceived by many, including many scientists, to be all but infallible.

The perception is validated by compelling news accounts in which a DNA specimen is the magic bullet, so to speak, that leads inexorably to the perpetrator. Media accounts of criminal forensics read like a script from an episode of the American television series CSI: Crime Scene Investigation.

Under optimum circumstances DNA is an extraordinarily precise forensic tool. However, the collection and analysis of DNA evidence is a human endeavor. It is susceptible to human fallibility-and venality-and this scientific fact has not been given sufficient consideration in the rush to create ever larger DNA databanks.

There is a growing body of research that demonstrates that error can and does occur with extraordinary frequency. Professor William C. Thompson has observed that the problem is widespread; that it occurs even in the best labs; and that forensic scientists have downplayed the scope of the problem and its import.[2] Thompson and his colleagues warn of “limitations or problems that would not be apparent from the laboratory report, such as inconsistencies between purportedly ‘matching’ profiles, evidence of additional unreported contributors to evidentiary samples, errors in statistical computations and unreported problems with experimental controls that raise doubts about the validity of the results.”[3]

The problem is not mere negligence-mislabeling and cross-contamination of DNA samples, and computational mistakes-but also unconscious bias and something more sinister: the intentional misrepresentation of DNA analyses.

The routine use of forensic DNA in criminal investigations and prosecutions poses novel and complex challenges to the integrity of the criminal justice system. A former district attorney in Manhattan put the issue this way:

DNA databanks do help apprehend dangerous criminals (and thereby prevent crime). But most people aren’t violent criminals and never will be, so putting their DNA on file exposes them to risks that they otherwise wouldn’t face. First, people who collect and analyze DNA can make mistakes.  … Second, people can be framed by the police, a rival or angry spouse. Third, DNA is all about context; there may be innocent reasons a person’s DNA is at a crime scene, but the police are not always so understanding.[4]

A major study by the British Journal of Criminology finds that at a certain point there are diminishing returns to society, in terms of public safety, from the inclusion of DNA samples in a massive databank. The report raises concerns about the “tactical” use of DNA when interviewing suspects, and about police officers with insufficient knowledge of forensics resorting to DNA evidence in lieu of rigorous detective work.[5]

And, of course, these issues also pose a formidable challenge to the integrity of forensic science.

In a 2009 report the National Academy of Sciences issued a sweeping critique of the nation’s crime labs in the United States, observing that forensic scientists with law enforcement agencies “sometimes face pressure to sacrifice appropriate methodology for the sake of expediency.”[6] Other researchers have observed that lab technicians typically fail to take measures to “blind” themselves to the expected outcome of their analysis. Studies of this phenomenon indicate that when faced with ambiguity in the information presented in a DNA sample, crime lab analysts will often fit their interpretations to support the prosecution’s theories.[7]

The proponents of an ever-expanding DNA databank dismiss such concerns, challenging the skeptic to demonstrate a wrongful conviction caused by error or abuse related to the use of DNA evidence. But this defense poses the wrong question. The pertinent question is this: Are there sufficiently rigorous and independent quality assurance procedures to ensure that error and abuse will be discovered; and if it is, will rigorous case review follow, along with sanctions and discipline if negligence or wrongdoing are involved? The answer is no.

If the foregoing is not sufficient to give pause, consider that twenty-five states require persons arrested to provide a sample for inclusion in a databank. Sixteen states now authorize law enforcement to investigate the family members of an individual whose DNA does not match crime-scene evidence, but is a near match. The scientific rationale for this practice is that a “partial match” between a crime-scene sample and the DNA of someone in the state’s databank may implicate a blood relative of that individual. This practice is aptly named: familial searching.

Consider this thought experiment: What is the race of the individual wrongfully convicted in the Las Vegas Police Department video? African American. To the extent error or fraud taint criminal investigations, the consequences-including wrongful prosecution and conviction-will be borne overwhelmingly by persons of color. The criminal justice system is not race neutral. The gross racial disparities in the population incarcerated for drug offenses are but one example of this fact.

So what’s to be done? What is a reasonable, prudent response to the emergence of this CSI counter narrative?

First, it is incumbent upon policy makers to undertake a rigorous and objective reexamination of the assumptions that have informed government’s creation of an ever-expanding DNA databank. The scientific community must play a central role in framing the terms of this debate.

Second, policy makers must create a robust regulatory model that dictates rigorous quality assurance protocols; standards for the accreditation and review of lab performance; methodologies for evaluating the outcome and resolution of criminal investigations that involve forensic DNA; and procedures for protecting the privacy and due process rights of defendants.

A 2009 Supreme Court ruling reflects perhaps a growing awareness that advances in forensic science are no guarantee of justice or fairness. In that case (affirmed in a 2011 ruling) the court held that lab reports may not be used at trial as evidence of a person’s guilt unless the analysts who created the reports testify in court, subject to cross-examination. This requirement, Justice Antonin Scalia observed, “is designed to weed out not only the fraudulent analyst, but the incompetent one as well.” The right to confront witnesses would be required by the Constitution, Justice Scalia concluded, even “if all analysts possessed the scientific acumen of Mme. Curie and the veracity of Mother Theresa.”[8]

Robert A. Perry, JD, is Legislative Director of the New York Civil Liberties Union.



1. The video can be viewed at
2. See Willliam C. Thompson, “Tarnish on the ‘Gold Standard’: Recent Problems in Forensic DNA Testing,” The Champion, January/February 2006.
3. See William C. Thompson, et al., “Evaluating Forensic Evidence: Essential Elements of a Competent Defense Review,” The Champion, April 2003. (Part 2 of this article appeared in the May 2003 issue of The Champion.)
4. Harlan Levy, “Caught Up in DNA’s Growing Web,” New York Times (op ed), March 17, 2006.
5. Carole McCartney, “The DNA Expansion Programme and Criminal Investigation,” British Journal of Criminology, October 25, 2005 [Published by Oxford University Press on behalf of the Centre for Crime and Justice Studies (ISTD)].
6. Adam Liptak, “Justices Rule Lab Analysts Must Testify on Results,” New York Times, June 26, 2009.
7. See William C. Thompson, et al., “Evaluating Forensic Evidence: Essential Elements of a Competent Defense Review,” The Champion, April 2003. (Part 2 of this article appeared in the May 2003 issue of The Champion.)
8. Melendez-Diaz v. Massachusetts, 557 U.S. _____ (2009)

© 2014 Forensic Genetics Policy Initiative