The forensic psychiatrist whose testimony about a TV show episode led to Andrea Yates' 2002 murder conviction being overturned took the witness stand Thursday in her retrial for the bathtub drowning of her children.

Dr. Park Dietz, who evaluated Yates in November 2001, began by recounting his professional experience.

In the first trial, he told jurors Yates knew drowning her five children was wrong. But Dietz, who had been a consultant for the "Law & Order" television series, also testified that one episode showed a woman being acquitted by reason of insanity after drowning her children in a bathtub. No such episode existed, and Yates' conviction as overturned because of the erroneous testimony.

Yates has again pleaded innocent by reason of insanity.

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Her attorneys say she suffered from severe postpartum psychosis and did not know her actions were wrong. Prosecutors argue that Yates did know drowning the children was wrong and therefore didn't meet the state definition of insane.

Yates killed her oldest son, 7-year-old Noah, last because she knew he would struggle the most and might have alerted the others to escape, Dr. Harry Lee Wilson testified Wednesday.

She held 3-year-old Paul, 2-year-old Luke and 5-year-old John under water, then carried their limp bodies to a bed. She also drowned 6-month-old Mary before drowning Noah, taking the baby's body to the bed but leaving him floating in the tub.

Yates used "a sequential approach, doing one after another, privately, secretively," said Wilson, a pediatric pathologist who reviewed the autopsy and crime scene photos and Yates' police confession. "The behavior was organized and methodical."

Wilson also testified Wednesday that Yates held the children under water for about three minutes before they became unresponsive, but the four youngest were still alive when she placed them on the bed. He said they lived for another three to six minutes.

At least 20 bruises on their arms, legs and heads shows they struggled as she held them under, he said, especially Noah, whose death was prolonged because he also raised up and gasped for air a few times, according to the evidence.

"Noah's body speaks to us of the struggle not to die," Wilson said.