Behavioral Genetics Evidence in Criminal Cases: 1994-2007

Abstract

In 1994, convicted murderer Stephen Mobley spurred an international debate on the political and scientific acceptance of behavioral genetics evidence in the criminal law when he fought to be tested for genetic deficiencies in an effort to appeal his death sentence. Such legal-scientific disputes are even more relevant today, given the relative upswing in the use of genetics evidence in criminal cases. This upswing also prompts a key question: How have courts and litigators treated behavioral genetics evidence in criminal cases since Mobley's 1994 appeal? Much of the controversy concerning Mobley was based on the presumption that behavioral genetics evidence would skyrocket in use and abuse. This chapter seeks to determine if such forecasts have been realized by analyzing forty eight criminal cases that relied on behavioral genetics evidence from 1994 to June 1, 2007.

These cases 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. Indeed, the overview suggests that, contrary to some commentators' warnings, the post-Mobley years have not revealed a legally irresponsible application of behavioral genetics factors in criminal cases. Rather, most courts continue to regard behavioral 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 either for denying defendants' offers of behavioral genetics evidence or for viewing such evidence in the worst light for defendants. For example, some courts have regarded a defendant's family history of behavioral disorder to be indicative of that defendant's potential for future dangerousness or misguided attempt to sidestep responsibility for violence. These kinds of judicial reactions suggest that at least some of the legal strategies using behavioral genetics evidence are without question a double-edged sword for defendants. Unwarranted constraints or stereotypical perspectives on the admissibility of behavioral genetics factors in death penalty cases can undercut some defendants' efforts to fight their executions through the use of traditional mitigating evidence. As a result, the criminal justice system may be undermining the very principles and progressive thinking the cap on behavioral genetics information was originally intended to achieve.