Criminal Insanity – The Impact of Legal Definitions

This paper will first seek to review the forensic psychology case of Jeffrey Dahmer, specifically his potential psychological diagnoses of Sexual Sadism and Asperger’s Disorder, as related to two legal definitions for the insanity defense.  The diagnostic criteria for Sexual Sadism according to the DSM-IV-TR require that a person “over a period of at least 6 months, recurrent, intense sexually arousing fantasies, sexual urges, or behaviors involving acts (real, not simulated) in which the psychological or physical suffering (including humiliation) of the victim is sexually exciting to the person” and “the person has acted on these sexual urges with a nonconsenting person, or the sexual urges or fantasies cause marked distress or interpersonal difficulty” (American Psychiatric Association, 2000, p. 574).  The diagnostic criteria for Asperger’s Disorder according to the DSM-IV-TR include “qualitative impairment in social interaction” and “restricted repetitive and stereotyped patterns of behavior, interests, and activities” where there is clinically significant impairment without delay in language and without cognitive developmental delay (American Psychiatric Association, 2000, p. 84).  Finally, this paper will evaluate the impact of the legal definition of insanity on the Yates v. Texas case and draw conclusions about legal definitions and their influence on case outcomes.

According to this week’s case study (2012), Jeffrey Dahmer was indicted in 1991 for 17 murders committed between 1978 and the date he was arrested for an assault against what would potentially have been his 18th victim.  Evidence collected by investigators would show that his murder victims suffered torture, sexual assault, cannibalism, and necrophilia at the hands of Dahmer.  His apartment was found to have contained body parts of his victims including four heads, several severed hands, and several severed penises.  Mental health experts working for both the prosecution and the defense examined Dahmer prior to his two-week long trial that was held in January of 1992.  The range of diagnoses provided by those experts included substance-related disorders and sexual disorders to include necrophilia, and sexual sadism, and other paraphilias.  One of the mental health experts testified that Jeffrey Dahmer would not be able to resist the urges generated by his sexual sadism.  While Dahmer plead not guilty by reason of insanity, he was found guilty and was sentenced to fifteen life terms in prison.  Any chances he may have had for parole were thwarted when he was murdered by another inmate at the Columbia Correctional Institute in Wisconsin.

Silva, Ferrari, and Leong (2002) reported in their case study a number of psychologically-significant abnormalities during Jeffrey Dahmer’s childhood and adolescence.  A fascination with bones and other body parts was reported as early as age four with an interest in taxonomy and the preparation of skeleton exhibits thoroughly developed by high school.  Dahmer’s elementary school years were marked by shy behavior, reclusiveness and an apparently limited range of emotional expression.  While he would maintain a notable social ineptness, Dahmer had reportedly exposed himself sexually to others during adolescence with reports of having masturbated in public on at least several occasions.  The end of Dahmer’s adolescence and his early adulthood were marked by recurring depression and suicidal ideation which were treated with antidepressants.  Dahmer enlisted in the United States Army but was discharged two years later due to alcohol-associated difficulties that included belligerence when drinking. Based on their compiled case history, Silva, Ferrari, and Leong (2002) argued that Jeffrey Dahmer appeared to have suffered from Asperger’s Disorder which they believed to be causally related to his necrophilic behaviors as a “sexualized form of the repetitive behavioral patterns typically encountered in Asperger’s Disorder” (p. 4).

Current U.S. federal law, in defining the insanity defense, states that “[it] is an affirmative defense to a prosecution under any Federal statute that, at the time of the commission of the acts constituting the offense, the defendant, as a result of a severe mental disease or defect, was unable to appreciate the nature and quality or the wrongfulness of his acts. Mental disease or defect does not otherwise constitute a defense” (18 USC § 17 (a)).  Sexual Sadism and Asperger’s Disorder, individually and comorbidly, would meet the requirement of a severe mental disease or defect.  However, Dahmer may not have been able to fully understand the wrongfulness of his actions through disordered justification as manifested by his psychological disorders.  Based on the U.S. statutory definition for the insanity defense, it would have been understandable for a court reviewing Dahmer’s case to accept an insanity plea.

The American Law Institute’s Model Penal Code defines insanity as where “[a] person is not responsible for criminal conduct if at the time of such conduct as a result of mental disease or defect he lacks substantial capacity either to appreciate the criminality of his conduct or to conform his conduct to the requirements of the law” (Week 5 Case Study, 2012, para. 3).  Here again, Sexual Sadism and Asperger’s Disorders, individually and comorbidly, meet the requirement of a mental disease or defect.  The divergence from the federal definition is in wrongfulness versus criminality.  While Dahmer may not have been able to fully understand the wrongfulness of his actions, his history of encounters with the criminal justice system combined with his reported functional intelligence would not necessarily render him unable to appreciate the criminality of his actions.  Based on the model penal code definition for the insanity defense, it is understandable how the court in Dahmer’s case was able to reject his insanity plea and render the guilty verdict that resulted in Dahmer’s incarceration.

J. Ray Hays reviewed for the National Psychologist (2002) the capital murder conviction in Texas of Andrea Yates for drowning her five children in 2001. Yates had significant mental health history involving numerous hospitalizations and years of outpatient treatment. Her treating psychiatrist had discontinued her neuroleptic medication for postpartum depression several weeks before she committed the murders.  Treatment by psychotropic medications resolved the initial question of adjudicative competency.  Yates raised the insanity defense under Texas law, which only requires that “at the time of the conduct charged, the actor, as a result of severe mental disease or defect, did not know that his conduct was wrong” (Texas Penal Code § 8.01).  Hays (2002) argued that both the psychiatrist testifying for the prosecution and the psychiatrist testifying for the defense erred in their testimony due to having been brought in from out of state and not understanding the laws of Texas.  Dr. Phil Resnick, the defense’s psychiatrist, told jurors that Yates knew her actions were illegal but she did not think it was wrong due to delusional, psychotic thinking.  Dr. Park Dietz, the prosecution’s psychiatrist, included information from the adjudicative competency examination as part of his criminal responsibility assessment in violation of forensic psychological ethics and the laws of the State of Texas.  The errors of the forensic mental health experts notwithstanding, the jury found Andrea Yates guilty of two counts of capital murder.  Four years later during appellate review, the convictions were reversed and remanded back to the court for new trials due, in part, to “the factual sufficiency of the evidence to support the verdict rejecting the insanity defense” (Yates v. Texas, 2005).  In 2006, a new jury found Yates not guilty by reason of insanity.



While the mental health professions generally agree upon the diagnoses of mental illness through the diagnostic criteria found in the DSM-IV-TR regardless of geographic location and macroecology, the impact of mental health on the realm of jurisprudence will be notably impacted by the definitions of law that may have slight variations from jurisdiction to jurisdiction.  Due to these variations, similar patients among various jurisdictions may have unequal access to a defense raised as a result of severe mental illness, notably psychotic disorders.  As such, the forensic mental health practitioner should remain cognizant of the legal definitions and mental health expectations in use on a case by case basis.



American Psychiatric Association. (2000). Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision. Arlington, VA: American Psychiatric Association.

Hays, J.  (2002).  State of Texas. v. Andrea Yates.  Retrieved from The National Psychologist at:

Silva, J., Ferrari, M., & Leong, G. (2002). The Case of Jeffrey Dahmer: Sexual Serial. Journal of Forensic Sciences, 47(6).

Week 5 Case Study.  (n.d.).  Retrieved on April 3, 2012, from Walden University at:

Yates v. Texas, 01-02-00462-CR (First District of Texas Court of Appeals, 2005).

© 2012 – 2014, Jeremy Liebbe. All rights reserved.

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About the author

Jeremy Liebbe holds a Master of Science in Forensic Psychology, holds a Bachelor of Arts in Police Science, and is currently completing a Doctorate of Philosophy in Psychology. He has over a decade of law enforcement investigative experience as a detective sergeant with experience including narcotics, crimes against children, and homicide investigations. As a result of his expertise in complex criminal investigations and forensic mental health Jeremy has earned numerous commendations, lectured throughout Texas and in several other states, authored and co-authored over a half dozen published papers, and has provided expert testimony in over a dozen felony trials.