HOUSTON (AP) -- Andrea Yates believed demons surrounded her and she was fulfilling a prophecy by drowning her five children last June, a jail psychiatrist testified Friday.
"She believed that the children would be tormented and perish in the fires of hell unless they were killed," Dr. Melissa Ferguson testified, saying Yates was "one of the sickest patients I have ever seen."
The testimony came as Yates' lawyers began making their case to jurors that she is innocent of capital murder by reason of insanity. Yates, 37, faces the death penalty if convicted.
Ferguson, recounting notes she made at the Harris County Jail June 21, a day after the children were drowned in a bathtub, said Yates screamed to her, "I was so stupid."
"Couldn't I have killed just one to fulfill the prophecy?" Yates asked. "Couldn't I have offered Mary?"
Six-month-old Mary was her youngest child.
During the examination, Yates moaned, cried and pulled at her hair, Ferguson testified. When Yates stopped screaming, she asked for a razor to shave her head. As she made the request, Yates pointed to where she continually picked at her scalp.
"She told me she wanted a razor to see if the marks are still there," Ferguson said. "She referred to them as the marks of the beast and 666."
Yates talked about President George W. Bush, former Texas governor, saying she could not destroy Satan and that "Gov. Bush would have to destroy Satan," Ferguson said.
Yates also believed her death would result in a prophecy's fulfillment, the psychiatrist said.
The severe depressive disorder Yates was diagnosed with started in the postpartum period, Ferguson said, and the delusions continued in the days after her arrest, although Yates was taking an antipsychotic drug.
When Ferguson told Yates on June 25 her mind was playing tricks on her, Yates said she was not mentally ill and that her experiences were real.
The following day, Yates refused to use soap in the shower and reported seeing Satanic images of teddy bears and ducks in the cell walls, Ferguson said. On June 27, Yates said she heard a man's voice insulting her and believed she was under constant surveillance.
Before Ferguson began testifying Friday, prosecutors finished their case by calling Dr. Harminder S. Narula, an assistant medical examiner who testified about his autopsy of the oldest Yates child, 7-year-old Noah.
Narula said Noah's head, arms and legs had recent bruising likely caused by someone holding him down. Some autopsy photos were shown to the jury Friday but not to Yates or anyone else in the courtroom.
Other medical examiners testified Thursday about John, 5, and Mary.
Yates is on trial only for those three deaths. Prosecutors have said she could be tried later for the deaths of the other two children, Paul, 3, and Luke, 2.
Dr. Patricia J. Moore, a medical examiner who performed autopsies on John and Mary, testified the children's heads had small bruises, likely from someone holding them under water.