Andrea Yates softly said "not guilty" Monday as her retrial began on charges that she drowned her five children in a bathtub just over five years ago.

As they did in her 2002 murder trial, the first police officers at Yates' house described a horrific scene of lifeless young bodies on a bed, one in a bathtub, and a woman in dripping wet clothing who opened the door and said, "I just killed my kids."

The prosecution and defense are expected to call most of the same witnesses, including the psychiatrist whose erroneous testimony led an appeals court to overturn her convictions.

Officer David Knapp, the first at the scene, testified that as he followed Yates inside her house June 20, 2001, he saw two sets of wet footprints on the tile floor leading into the bathroom, indicating one of the children had escaped the bathtub before she caught him.

Officer Frank Stumpo told jurors he saw the lifeless bodies of 5-year-old John, 3-year-old Paul, 2-year-old Luke and 6-month-old Mary on the bed. The oldest, 7-year-old Noah, was still in the bathtub.

Yates has again pleaded not guilty by reason of insanity. Her attorney George Parnham does not dispute that she killed the children but says she suffered from severe postpartum psychosis and did not know her actions were wrong.

Prosecutor Kaylynn Williford said in her opening statement that Yates' actions and admissions belie those claims.

"She had been contemplating for approximately two years that she knew it was wrong, that she knew she would be punished, and that's what she told police on June 20, 2001," Williford said.

She said Yates waited to drown the children until her husband, Rusty, went to work and before her mother-in-law arrived to help care for the youngsters. The small bruised bodies show how she held down the struggling children in the water, Williford said.

Parnham said Yates told a jail psychiatrist after her arrest that the only way she could save her children and send them to heaven was to kill them because she was a bad mother and Satan was living inside her. Yates also told the psychiatrist she was hearing demons in jail and thought there was a "666," a symbol of the Antichrist, on her scalp.

Parnham also said that Yates had been in a mental hospital in March and April 2001, but that in the weeks before the drownings, "for some inexplicable reason," a doctor had told her to stop taking a powerful drug.

"But for Andrea Yates being taken off anti-psychotic medications, those children would be alive today," Parnham said.

Prosecutors say they will again call Dr. Park Dietz, the psychiatrist who testified that Yates knew her actions were wrong. Dietz, also a consultant to the "Law & Order" television series, told jurors that one episode depicting a woman who drowned her kids in a bathtub — and was acquitted by reason of insanity — aired before the Yates children died.

But no such episode existed, attorneys learned after Yates was convicted but before jurors sentenced her to life in prison. That mistake caused an appeals court in Houston last year to overturn Yates' conviction.

As in the first trial, Yates is being tried only in the deaths of Mary, John and Noah, a common practice in cases of multiple slayings.

If convicted, she will be sentenced to life in prison. Because the first jury rejected a death sentence and prosecutors have found no additional evidence, they cannot seek Yates' execution.

If found not guilty by reason of insanity, she could be committed to a state hospital, with periodic hearings to determine whether she should be released.

Yates is being jailed during the trial, which is expected to last about five weeks. She had been in a state mental hospital since February, when she was released from incarceration on bond for the first time since the killings.