Revisiting the Legal Link between Genetics and Crime

50 Pages Posted: 6 Sep 2006


In 1994, convicted murderer Stephen Mobley's death penalty case attracted intense international debate when his attorneys attempted to have Mobley tested for genetic deficiencies based on his family history of disorders. According to the attorneys, indications that Mobley shared a genetic propensity for serious misconduct could help explain some of his troubling tendencies and why he should not be executed. Ultimately, the trial and appellate courts rejected that reasoning. In 2005, Mobley was executed. Yet Mobley's death once again stirs the genetics and crime debate with a key question: How have courts and litigators treated genetics evidence in criminal cases during the years following Mobley's first trial? Much of the controversy concerning Mobley v. State was based on the presumption that such evidence would skyrocket in use and abuse. This article seeks to determine if such forecasts have been realized.

Contrary to predictions at the time of Mobley's appeal, it appears that little has occurred in the area of genetics and crime warranting the concern that Mobley generated. Of course, the criminal justice system should remain alert to potential hazards of genetics evidence. Yet unsupported fears could also curtail some defendants' constitutionally legitimate attempts to submit aggravating factors in their death penalty cases, in particular, genetics evidence that could validate the existence of more traditionally accepted mitigating conditions, such as mental illness. Presumably, judges and juries would be less likely to think that a defendant is feigning states such as schizophrenia or alcoholism if such disorders commonly occurred across generations of the defendant's family.

Part I of this article briefly reviews the facts and legal arguments in Mobley. Part II addresses the primary issues that concerned the court in Mobley, noting that many of the original reasons for the controversy over the potential use of genetics evidence remain the same as they did in 1994. Part III discusses the twenty-seven key genetics and crime cases occurring between 1994 and 2004, since Mobley spurred the topical dispute. These cases, which are surprisingly small in number, share several important characteristics: they overwhelmingly constitute murder convictions in which defendants attempted to use genetics evidence as a mitigating factor in a death penalty case (as Mobley did), and the evidence is introduced mostly to verify a condition (such as a type of mental illness) that is commonly acceptable for mitigation. Part IV contends that, contrary to some commentators' warnings during the first Mobley trial, the last decade has not revealed a legally irresponsible application of genetics factors in criminal cases. Rather, courts continue to regard genetics variables skeptically, and society still embraces the same political and moral concerns over the role of such information. At the same time, courts have failed to provide sound and conceptually consistent reasons for denying defendants' offers of genetics evidence.

This article concludes that unwarranted constraints on the admissibility of genetics evidence in death penalty cases can undercut some defendants' efforts to fight their executions. By imposing unreasonable limitations on genetics arguments, the criminal justice system may be undermining the very principles and progressive thinking the cap on genetics evidence was originally intended to achieve.

Suggested Citation

Denno, Deborah W., Revisiting the Legal Link between Genetics and Crime. Law and Contemporary Problems, Vol. 69, pp. 209-257, 2006, Fordham Law Legal Studies Research Paper No. 928463, Available at SSRN:

Deborah W. Denno (Contact Author)

Fordham University School of Law ( email )

Fordham University School of Law
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New York, NY 10023
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