Houston ? Andrea Yates was legally insane when she drowned her five children in the family bathtub last June, a psychologist testified Tuesday at her capital murder trial.

Dr. George Ringholz, a neuropsychologist from Baylor College of Medicine, said he reached that conclusion after studying her medical and family history and tests he conducted on the 37-year-old woman.

A small stuffed dog, beads and a packet of candy sit on the stone marking the grave of John Samuel Yates, 5, in Webster, Tex. The marble marker is one of five identical stones around the one large headstone bearing photos of each of the Yates children. Their mother, Andrea Yates, is on trial in Houston for their deaths.

“Mrs. Yates was severely ill and in the course of an acute psychotic episode,” Ringholz said in his second day on the witness stand. “She did not know the actions she took on that day were wrong.”

Yates has pleaded innocent by reason of insanity. If jurors accept Ringholz’s assessment, it could save her from life in prison or death by injection.

To prove insanity, Yates’ lawyers must show the Houston woman suffered from a severe mental disease and didn’t know the difference between right and wrong at the time of the drownings.

Prosecutors argue Yates was sane when she killed her children and they are seeking the death penalty.

Ringholz testified Yates suffered from schizophrenia and was totally unaware of her actions. She had significant impairment in functioning and displayed many signs of the illness, including hallucinations, delusions, incoherence and isolation, he said.

Yates is being tried on two counts of capital murder in the deaths of 7-year-old Noah, 5-year-old John and 6-month-old Mary. Charges eventually could be filed in the deaths of Paul, 3, and Luke, 2.

If jurors determine Yates is innocent but insane, a hearing will be held at which she either will be released or involuntarily committed.

If jurors convict her, they must determine whether she poses a future danger to society and if there is enough mitigating evidence to sentence her to life in prison rather than death.