Andrea Yates received messages from cartoons and believed that drowning her five children would result in the destruction of Satan, a jail psychiatrist testified during her capital murder trial.

"She believed that the children would be tormented and perish in the fires of hell unless they were killed," Harris County Jail psychiatrist Dr. Melissa Ferguson testified as Yates' defense got under way Friday.

Yates, 37, faces two capital murder charges in the June 20 drowning deaths of three of her five children. Defense attorneys say she is innocent by reason of insanity.

Yates faces the death penalty if convicted.

Ferguson, who said she has examined more than 6,000 mentally ill people in 16 years, described Yates as "one of the sickest patients I have ever seen."

Ferguson diagnosed the former nurse as psychotic and suffering from hallucinations. But Yates said she wasn't mentally ill and didn't need medication, the psychiatrist said.

Yates told Ferguson her experiences were real, and that cartoon characters told her she was a bad mother just days before she drowned her children.

Recounting her medical notes from the day after the children died, Ferguson said Yates screamed to her, "I was so stupid!"

"Couldn't I have killed just one to fulfill the prophecy?" Yates said. "Couldn't I have offered Mary?"

Mary, at 6 months, was the youngest child to die.

When she stopped screaming, Yates asked Ferguson for a razor to shave her head, the psychiatrist testified. 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 Bush, the former Texas governor, saying she could not destroy Satan and that "Gov. Bush would have to destroy Satan," Ferguson testified.

Yates believed her death would result in the prophecy's fulfillment, the psychiatrist said.

"I deserve to be punished," Yates told Ferguson. "I am guilty."

The psychiatrist said Yates claimed to have heard human voices that told her to grab a knife and harm her children.

"In her mind, she was marked by Satan," the psychiatrist said.

The severe depressive disorder started following Mary's birth in November 2000, Ferguson said. Yates continued to suffer delusions in the days following her arrest, even though she had been taking an antipsychotic drug, the psychiatrist testified.

When Yates called police to her Houston home, officers found 7-year-old Noah, her oldest child, floating face down in the bathtub. The bodies of her four youngest children, clad in pajamas, were on their parents' bed, the sheets soaked.

Yates told a police investigator on the day of the drownings she had thought about hurting her children for at least two years.

Defense attorneys say Yates suffered from a severe mental disease and did not know the difference between right and wrong at the time of the drownings.

Prosecutors, who finished their case Friday, claim Yates knew her conduct was wrong.

Yates is on trial for the deaths of Noah, 5-year-old John, and Mary. Charges could eventually be filed in the deaths of her other two children.