A Houston woman accused of systematically drowning her five young children will likely plead innocent by reason of insanity, according to her attorney.
Andrea Yates, 36, was arrested last week in what a prosecutor called "the most horrendous thing that I've ever seen."
Yates told police Wednesday that she drowned her children one by one in a bathtub in their suburban Houston home. Those killed have been identified as Noah, 7; John, 5; Paul, 3; Luke, 2; and Mary, 6 months.
Yates has been charged with one count of capital murder for the deaths of Noah and John. Authorities said other charges might follow.
Houston attorney George Parnham, who represents Yates, said he has talked with psychiatrists treating her at the Harris County Jail.
"I've accumulated evidence in the last 24 hours that strongly suggests that the mental status of my client will be the issue, which means entering a not guilty plea by reason of insanity," Parnham said in Sunday editions of the Houston Chronicle.
He would not say what evidence indicated she was insane when she killed the children at her Clear Lake home. Parnham also declined to say anything about the current mental state of Yates.
Meanwhile, Russell Yates, her husband, remains one of her strongest supporters. He told reporters on Thursday that her severe postpartum depression, coupled with her father's recent death, drove her to harm their children.
George Dix, a law professor at the University of Texas, said insanity defenses are rarely used, and those that are used rarely succeed. To be found innocent by reason of insanity, Andrea Yates would have to show that she was so mentally impaired that she couldn't see circumstances for what they were.
For example, if she "believed her children to be devils, she's entitled to acquittal," Dix told the Dallas Morning News in Sunday's editions.
"Homicide consists of causing the death of another person," Dix said. "If you believe the thing you destroyed was not a person, the verdict is your conduct wasn't criminal."
Three years ago in Houston a jury acquitted Evonne Rodriguez of capital murder in the beating and strangling death of her 4-month-old son. Rodriguez told authorities she thought her son was possessed by demons, so she threw his body in Buffalo Bayou.
A judge sent Rodriguez to a state mental hospital.
Michelle Oberman, a law professor at DePaul University in Chicago and author of Mothers Who Kill Their Children, which will be released in August, said postpartum depression has been a defense element in cases where mothers kill their children since the mid-1980s.
"The best chance she has, if she's got any good chance, lies in hoping the jury understands the circumstances under which she was operating and to understand the reality of postpartum depression," Oberman told the Dallas newspaper.
About 10 percent to 20 percent of mothers face some level of postpartum depression. Most cases are mild, and can be treated with counseling and medicine. Some cases are severe, causing psychosis or delusions.
Russell Yates visited his wife in jail on Friday. During a candlelight vigil later that evening, he asked people to pray for her.
"That will help a lot. She's suffering," he said tearfully.
Parnham said he is working with Russell Yates and her mother and brothers in an attempt "to get beyond the grief that obviously is the result of this tragedy."
Funeral services for the children, who ranged from 6 months to 7 years old, have been scheduled for 10:30 a.m. Wednesday at Clear Lake Church of Christ.
The Associated Press contributed to this report