Forensic Psychology Expert Witness & The Insanity Defense

Robert Rigg, associate professor and director of the Criminal Defense Program at Drake University Law School in Des Moines, says that “Jurors don’t like the insanity defense.” In fact, only a few cases in the state have succeeded with an insanity or diminished-capacity defense, according to Rigg, who has worked on a dozen or so over the past 31 years. Defense attorneys and law professors agree that the insanity defense is difficult and jurors are skeptical. It comes down to a “battle of the experts.” The forensic psychology expert witness for the defense testifies that the accused has a mental disease, the state counters with an expert who finds the person sane and the jury has to decide which diagnosis is credible.

University of Iowa law professor David Baldus says that not every kind or degree of mental disease or disorder will excuse a criminal act. Iowa code is specific – a person must suffer from a “diseased or deranged condition of the mind” that renders the person either incapable of knowing or understanding the nature and quality of his act or incapable of distinguishing right and wrong.

This is what Mark Becker, 24, accused of shooting Iowa football coach Ed Thomas to death, faces in his first-degree murder trial set for September. He filed this week his intent to claim insanity and/or diminished responsibility as a defense. Becker’s is the latest in a recent string of insanity defenses.

Excerpted from