Yates trial highlights power of an expert witness

As reported in USA Today

During the murder trial of Andrea Yates in 2002, only one of a dozen mental health experts who testified concluded that the Houston mom was legally sane when she drowned her five children in the family bathtub.

That witness, called by prosecutors, was Park Dietz, a renowned forensic psychiatrist. As the prosecutors' only mental health expert, Dietz and his testimony helped convict Yates. The conviction later was overturned. When Yates is retried beginning Thursday, much of the attention again will be on Dietz, who is back on the prosecution's witness list. And now, there are questions about Dietz's conclusions in the Yates case because of his testimony in another trial involving a Texas mother who killed two of her children.

From the Side Bar article:

When the Texas Court of Appeals threw out Andrea Yates' conviction last year and set the stage for a retrial, it blamed Park Dietz, the prosecution's mental health expert.

During Yates' trial in 2002, Dietz testified that he believed Yates was legally sane when she drowned her five children the previous year. The jury agreed, found Yates guilty and gave her a life sentence.

It was Dietz's testimony on a separate matter that led the appeals court to overturn Yates' conviction.

On the witness stand, Dietz described an episode of the TV drama Law & Order in which a mother with postpartum depression drowned her children and was found not guilty by reason of insanity. The episode, Dietz testified, aired just before Yates drowned her children

In fact, there was no such episode of Law & Order.

Dietz did not testify that the show inspired Yates. But during closing arguments, prosecutors "connected the dots" to suggest the show had done just that, the appeals court said.

A grand jury investigated Dietz and the prosecutors but found no wrongdoing. Dietz says his testimony about the TV show was "an honest mistake."

This brings up all kinds of questions regarding the proper role of psychiatry in the legal system.

See also this article :

Inaccurate Expert Testimony Wins Yates New Trial

Though the state maintained that Dietz's testimony about the "Law & Order" episode "was not material," the appeals court agreed with Yates, finding that "the State used Dr. Dietz's false testimony to suggest to the jury that [Yates] patterned her actions after that `Law & Order' episode." The court emphasized that the prosecution's use of the false testimony did not equate to "prosecutorial misconduct" but did "give weight to that testimony."