HOUSTON — Andrea Yates suffered from a severe mental illness at the time she drowned her five children last year but knew her actions were wrong, a psychiatrist testified.

Dr. Park Dietz, a forensic psychiatrist hired by the state, testified at Yates' murder trial Thursday that she didn't act like someone who believed Satan ordered her to kill her children to save them from eternal damnation. Defense witnesses have said delusions and psychosis drove Yates to kill.

"I was pretty determined to do what (Satan) told me to do," Yates told Dietz in a videotaped interview in November. The tape was played in court Thursday.

"The fact that she regards it as coming from Satan is the first indication that she knows this is wrong," Dietz said. "She doesn't think this is a good idea that comes from God. She thinks it is an evil idea that comes from Satan."

Dietz said Yates didn't seek out a priest or minister, call the police, send her children to a safe place or attempt suicide to try to save her children.

"I do expect people with delusions of imminent harm to act as if that is true and protect the ones they love," Dietz said.

Yates, 37, who has pleaded not guilty by reason of insanity, faces murder charges in the drownings of 7-year-old Noah, 5-year-old John and 6-month-old Mary. Charges could be filed later in the deaths of Paul, 3, and Luke, 2. She faces life in prison or the death penalty if convicted.

Defense attorneys are trying to show Yates didn't know right from wrong when she drowned her children.

Dietz has worked on other high profile cases, including that of serial killer Jeffrey Dahmer, "Unabomber" Ted Kaczynski and South Carolina child killer Susan Smith. He was called as a rebuttal witness by prosecutors after the defense rested its case.

Dietz said Yates kept thoughts about killing her children a secret because she feared she would be stopped.

"Ordinarily when someone keeps a criminal plan secret they do it because it's wrong," he said. On the videotaped interview with Yates, Dietz asked her why Satan would want her to do something that would save her children from Hell's fires. She said the deaths would result in her being condemned.

"You saw it as a sin you were going to commit?" Dietz asked Yates during the Nov. 7 interview.

"Yes," she replied.

"Did you struggle against doing it?" the psychiatrist asked.

"No," Yates told him.

Dietz said Yates became confused and sometimes changed her story during the interview. He thought the changes came because Yates was still depressed and likely suffers from schizophrenia.

Dietz said a note in Yates' medical records showed Dr. Mohammad Saeed told her husband, Russell, in April that she should not be left alone.

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"When you have a mother who is this severely impaired, someone has to be with her at all times," Dietz said. "It isn't safe to leave her with the children."

Dietz said several things contributed to Yates' condition, including her refusal to take her medicine and her efforts to home-school her children inside a converted bus where the family lived in 1999.

Dietz said there were "repeated examples of Mrs. Yates not following the advice of her doctors and thinking she knows best."

Defense expert witness Phillip Resnick told jurors last week that Yates knew drowning her children was illegal, but in her psychotic mind thought it was the right thing to do.

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