Associated Press Andrea Yates, in this image from television, sits as her attorney George Parnham presents his opening arguments on Monday during the first day of Yates' trial for the killing of her five children.

HOUSTON - When Russell Yates learned his five children had been killed, he fell to the ground and then threw a chair across the yard, a police officer testified yesterday.

"I just thought it best for me not to talk to him," Houston Police Sgt. David Svahn said. "He was very, very upset."

He testified at the trial of Yates' wife, Andrea Yates, 37, who is charged with two counts of capital murder for the June 20 drownings and faces the death penalty. She has pleaded innocent by reason of insanity.

Svahn said he was the first to encounter the father after taking Andrea Yates into custody.

He said Russell Yates suddenly came running up to the house.

"He was screaming and hollering," Svahn testified. "He was saying, 'What did she do to my kids? What did she do to my kids?'"

Svahn said he asked the man what was going on.

"He said his wife had called him at work and told him it was time to come home," Svahn said. "His wife told him she had hurt all five of the kids and that she finally did it."

The officer said he then had the grim task of informing Russell Yates that his children were dead.

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

On Monday, the first day of the trial, Officer David Knapp said he followed Andrea Yates into the house after she summoned police, and in the bedroom he saw a child's arm protruding from under a wet sheet. Knapp lifted it and saw the lifeless bodies of Mary, 6 months, Luke, 2, Paul, 3, and John, 5. Noah, 7, was floating face down in the bathtub.

"She was standing behind me ... and I didn't hear her cry" or show any emotion, Knapp said.

Defense attorney George Parnham told jurors that Yates had a history of suicide attempts and was so psychotic that her delusions drove her to drown her children.

"Postpartum depression with psychotic features, as will be testified to from the stand, is the cruelest and most severe of mental illnesses," Parnham said.

But prosecutors say she knew her actions were wrong when she held each of her five children beneath the water in the bathtub until they stopped breathing.

"She knew this was an illegal thing," Harris County assistant district attorney Joe Owmby said during opening statements Monday. "It was a sin. She knew it was wrong."

Knapp said Yates answered his questions in a monotone voice and followed his instructions to sit down and show identification.

"Her eyes were wider than what I'd consider normal," Knapp said.

Frank Stumpo, the second Houston police officer who arrived at the house, testified that he asked Yates if she realized what she had done.

"Yes, I do," was Yates' response, the officer testified.

If Yates is found innocent, a hearing will be held to determine whether she will be released or involuntarily committed. If found guilty, jurors will have to determine if there is enough mitigating evidence to sentence her to life in prison rather than death.