Editor's Note: As part of CNN.com's new Crime section, we are archiving some of the most interesting content from CourtTVNews.com. This story was first published in 2006.
(Court TV) -- Andrea Yates' psychotic mind was like her own private battlefield in the war between good and evil, according to a defense expert who testified Thursday that Yates believed killing her five children would be a final defeating blow to Satan.
"It is my opinion, with medical certainty, that Mrs. Yates on June 20, 2001, believed she was doing what was right for the children. And in her heart, and even in her psychotic mind, she knew she was doing what was right," said Dr. Phillip Resnick, a forensic psychiatrist who evaluated Yates in 2001.
Yates is accused of drowning her five children, Noah, 7, John, 5, Paul, 3, Luke, 2, and Mary, 6 months. She has pleaded not guilty by reason of insanity.
Prosecution experts say that even if Yates were mentally ill, she knew that killing her children was wrong, and therefore, she does not meet Texas's legal standard of insanity.
"In my opinion, she did know what she did was illegal, even though she thought it was right," Resnick said.
Yates even expected to be executed, Resnick said, and her death would fulfill her delusional prophecy, as she believed Satan already had won the battle for her soul.
"Satan, the one and only Satan, not just a demon, but the singular Satan, would be executed ... It would fulfill the prophecy, the final battle, Armageddon," Resnick said.
He added that those who know their actions are wrong tend to wipe away fingerprints, wear disguises, and try not to get caught. But Yates hid nothing: She called 911 after the killings, and she cooperated with investigators, Resnick said.
Based on interviews and his study of the defendant's psychiatric records, Resnick said Yates believed killing her children was the only way to win her battle with Satan for her children's souls -- if she killed them while they were still under the "age of accountability," they would join God in Heaven.
Yates had a history of postpartum psychosis, major depression and two suicide attempts before she drowned her children and laid their bodies on her bed, covering them with a sheet. Noah, the eldest, was left floating face-down in the tub.
Before the killings, Resnick said, Yates saw messages in the movies "Seven" and "O Brother, Where Art Thou?" that she believed were Satan's personal torments.
"Innocent events -- anyone could go to a movie, but we wouldn't get the message that this was for us," Resnick said.
Prosecutors say Yates' decision to hide her homicidal plan from her family and friends indicates her guilt and proves that she knew her intentions were wrong.
Resnick said the concealment fit her delusions. She thought Satan could hear spoken words, he said, but could not read her mind.
She knew that friends, family and society at large would not approve of her decision, Resnick said, but Yates thought she was fighting a bigger battle, and had more information about how her children would falter because of her bad parenting.
"In other words, she had knowledge that John would grow up to be a serial killer, she had knowledge that Paul would be a deaf, mute, homosexual prostitute," Resnick said of Yates' delusions.
Resnick conceded during cross-examination that Yates expressed some ambivalence on the day after the killing about what she had done, as evidenced by her doubts to a therapist over whether her children had made it to heaven.
Prosecutors contend Yates killed her children because she didn't want to take care of them any longer. Resnick agreed that Yates had expressed being overwhelmed by having to manage and home-school such a large family.
Yates, 43, wore a green dress and tan flats as she sat at the defense table facing the jury. She was alert, but did not appear to be actively engaged in her case.
Resnick testified that he previously worked as a consultant for the defense in the Susan Smith murder trial -- the case of the South Carolina mother who rolled her car into a lake, killing her two sons.
Smith's defense did not call him to testify, Resnick said, after he concluded that Smith was not legally insane.
"Andrea Yates, would it be fair to say, is not a Susan Smith?" defense attorney George Parnham asked.
The question was stricken from the record.
A jury convicted Yates of murder in 2002, but a new trial was granted by an appeals court due to the erroneous testimony of a prosecution expert.
Yates is charged in three of her children's deaths and will be sentenced to life in prison if convicted.
If found not guilty by reason of insanity, she will be sent to a state psychiatric hospital and her case will be regularly reviewed. E-mail to a friend