Updated

A mother who smashed her sons' skulls with rocks had delusions that she and Andrea Yates (search), who drowned her children in 2001, were chosen by God to be witnesses after the world ends, a psychiatrist testified Tuesday.

Deanna Laney (search), a deeply religious stay-at-home mother who home-schooled (search) her children, has pleaded innocent by reason of insanity to charges of murder and causing serious injury to a child. She has said God told her to kill her children.

Psychiatrist Park Dietz testified Tuesday that Laney had delusions that she and Yates, a Houston woman who drowned her five children, would survive the end of the world to teach others about God. Dietz also testified for the prosecution in Yates' case.

"She thought she would be one of the two witnesses described in the book of Revelations (search)," Dietz told the jury.

Prosecutors contend that Laney knew right from wrong when she killed her children last Mother's Day weekend in the little town of New Chapel Hill, 100 miles southeast of Dallas.

But two psychiatric experts for the defense, two for the prosecution and one for the judge all have said Laney was insane according to the legal definition.

Dietz, who believed that Yates knew right from wrong when she killed her children, testified Tuesday that Laney did not. Yates was sentenced to life in prison in 2002.

Laney had delusions in which she would read everyday events or objects as messages from God. When her baby had abnormal bowel movements, for example, she thought it was a message from God that she was not properly "digesting" God's word, Dietz said.

"To interpret what a baby leaves in his diaper reflects a mentally ill person," Dietz said.

Laney had at least one other psychotic experience several years earlier in which she had hallucinations of smelling sulfur she believed was God's way of alerting her the devil was near, he said.

Earlier Tuesday, Laney's husband testified that he saw no change in his wife's mood before the attack and no clue that she was capable of killing the boys.

"I don't understand it," said Keith Laney (search), who has stood by his wife in court.

Keith Laney, 47, smiled at his wife when prosecutors asked what year they were married but briefly lost his composure at the sight of a poster-sized photograph of the three smiling boys, taken months before the killings.

The jury on Tuesday also saw a crime-scene video of 8-year-old Joshua and 6-year-old Luke, lying dead in a yard, near garden signs that read, "Mom's Love Grows Here" and "Thank God for Mothers." The boys were found in their underwear with heavy rocks on their chests.

The video also showed a large spot of blood in a baby bed, where Deanna Laney severely injured the couple's youngest son, Aaron, 14 months old at the time.

Laney, 39, lowered her head during the testimony and wept as graphic autopsy photos were shown to the jury of eight men and four women.

To show the severity of the attack on Joshua, prosecutor Matt Bingham hammered a 16-pound rock into the floor of the courtroom eight times. Vibrations were felt throughout the courthouse.

Prosecutors are not seeking the death penalty.