LOS ANGELES – The resume of psychiatrist Park Dietz (search) reads like a who's who of notorious killers of the last quarter-century.
The one-time FBI profiler has testified about criminals including Unabomber Theodore Kaczynski (search), serial murderer Jeffrey Dahmer and would-be presidential assassin John Hinckley Jr.
Now Dietz, often the go-to guy for prosecutors, is himself under the microscope. His erroneous testimony led a Houston appeals court on Thursday to overturn the murder conviction of Andrea Yates (search) for drowning three of her children.
It is an uncharacteristic black mark on a career expert witness whom courtroom friends and foes alike admire for his thoroughness and integrity.
"I absolutely believe he's not a bought-and-paid for (witness). He absolutely believes what he says and backs it up with work," said Gerald P. Boyle, Dahmer's defense lawyer. "I will never believe that he knowingly said anything that's a misstatement."
Dietz spent 18 hours interviewing Dahmer before testifying for the prosecution that he believed the serial killer could have stopped himself from murdering 17 young men and boys. In a telephone interview from Milwaukee, Boyle said his own defense psychiatrists held Dietz in "high regard," even as they disputed his conclusions.
In Yates' case, Dietz testified that while she may have been mentally ill, she also knew right from wrong when she killed her children.
But Dietz also told jurors that before the crimes occurred in 2001, an episode of the television show "Law & Order" aired about a mentally ill woman who drowned her children and was found innocent by reason of insanity.
Dietz, who has been a technical consultant for the show, suggested the Texas mother got the idea from the episode, but a defense lawyer later said he was told by the show's executive producer that no such episode ever aired.
Prosecutor Joe Owmby mentioned Dietz's reference to the episode in his closing arguments before jurors convicted Yates, but later said the psychiatrist had been confused and had erred.
The First Texas Court of Appeals ruled there is "a reasonable likelihood that Dr. Dietz's false testimony could have affected the judgment of the jury."
Dietz runs two consulting firms out of the wealthy Orange County suburb of Newport Beach. The companies' experts have testified in high-profile court cases and have advised hundreds of major corporations, government agencies and celebrities on how to prevent stalkers, school shootings, workplace mass murders and other threats.
He has sometimes irked mental health colleagues with his strict views on mental illness as a legal defense, and his contention that violent TV news, movies and TV shows inspire copycat sexual violence, school shootings and other crimes.
"With rare exceptions, people are responsible for what they do," he told Psychology Today in a 1999 interview. "Killers seldom meet the legal standard for insanity, which is quite different from the way most people use the word every day.
"Killers may be disturbed, but that doesn't necessarily mean that they can't tell right from wrong or are compelled to maim or murder."