Six weeks before she drowned her five young children in the bathtub, Andrea Yates filled the tub with water unexpectedly one day and said she "might need it," her mother-in-law testified.

Dora Yates, the first of the Houston woman's relatives to take the stand in her murder trial, said Tuesday that Andrea Yates was catatonic and "was not herself" for several months before the children were killed last June.

Andrea Yates, 37, could face the death penalty. She has pleaded innocent by reason of insanity.

Dora Yates, who wiped her eyes Tuesday when calling Andrea her "very precious daughter-in-law," said she left her home in Hermitage, Tenn., last April to visit her son's family in Houston for a week. But she ended up staying several months, she said, because Andrea was ill and needed help with the children.

Dora Yates told of a day last May when she found her daughter-in-law in the bathroom with a tub full of water. "I might need it," she quoted Andrea Yates as saying.

Defense attorneys suggested during opening statements Monday that Yates' delusions had caused her to fear the family's water supply might be interrupted.

Prosecutors say Andrea Yates suffered from a mental illness but knew the difference between right and wrong at the time of the drownings.

Several police officers have testified that Andrea Yates answered their questions on June 20, looked directly at them and read and signed a consent form for police to search the house.

Houston police Sgt. David Svahn testified Tuesday that Yates' husband, Russell, ran up to the house screaming that day after his wife called him at work and told him to come home.

Svahn said he had the grim task of informing Yates that his children, ages 6 months to 7 years, were dead.

"At that point he fell to the ground and began hitting his hand on the ground," Svahn said. The father then picked up a plastic chair from the yard and threw it, the officer said.

"His wife told him she had hurt all five of the kids and that she finally did it," Svahn said.

The day before the drownings, Dora Yates said, Andrea stood in front of the television for 45 minutes as the children watched cartoons but didn't interact with them or react to the program.

Dora Yates testified that she doubted her daughter-in-law knew right from wrong, "not in the state she was in," because she stared into space for hours, and even scratched her head until she had bald spots.

Andrea Yates normally was giving and comforting, but her depression grew worse after her father's death last March, Dora Yates said. Her arms trembled, her foot tapped and she smiled infrequently. When asked a question, Andrea didn't answer or waited a while before speaking, Dora Yates testified.

Yates said her daughter-in-law appeared somewhat better after a brief stay at a mental hospital last spring.

Harris County Assistant District Attorney Joe Owmby asked Dora Yates why she refused to talk with his office or expert witnesses in helping to determine whether Andrea Yates was sane at the time of the drownings.

"The prosecution is seeking the death penalty against my daughter-in-law, and I firmly think that is wrong," she said.

Yates is charged with murder for the deaths of three of her five children. Charges eventually could be filed in the deaths of the other two.

If Yates is found innocent by reason of insanity, a hearing will be held at least 30 days later, when she will either be released or involuntarily committed.

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