As Andrea Yates' capital murder trial enters its third week Monday, expert witnesses will present differing opinions on whether the stay-at-home mom knew right from wrong last summer as she admitted struggling to hold each of her children face down in a tub of water.

Yates, 37, faces two capital murder charges in the drownings of three of her five children.

Dr. Mohammad Saeed, the psychiatrist who treated Yates in the months prior to the drownings, is expected to take the stand Monday. Saeed last saw Yates two days before her children's deaths.

Yates called police and confessed to drowning her children June 20.

Defense lawyers say she is innocent by reason of insanity. An expert witness who testified for the defense last week told jurors Yates suffers from schizophrenia, which was worsened by her bouts with postpartum depression following the births of her fourth and fifth children.

Schizophrenia causes a person's thinking, feeling and behavior to become impaired. It includes symptoms such as delusions, hallucinations and social withdrawal.

Defense expert witness Phillip Resnick told jurors Friday that Yates knew her actions were illegal, but that she thought drowning her four sons and 6-month-old daughter was the only way to save them from hell.

Resnick said Yates thought she would be punished for her children's deaths and that the world would be saved from Satan, who she believed lived within her and would die when the state of Texas executed her.

Resnick is considered one of the nation's top forensic psychiatrists, having previously explored the inner workings of the minds of serial killer Jeffery Dahmer, Unabomber Ted Kaczynski and Susan Smith, a South Carolina mother sentenced to life in prison for drowning her two sons in 1994.

Resnick's counterpart, Dr. Park Dietz, has also explored the high-profile cases of Dahmer, Kaczynski and Smith. Dietz is expected to testify as a prosecution witness when the state begins presenting its rebuttal to Yates' insanity defense.

In Texas, a person is presumed sane.

Resnick, who is expected to undergo cross-examination Tuesday, told jurors last week that parents are driven to kill for a number of reasons, including revenge against a spouse, accidental mistreatment which leads to death or a child being unwanted.

Also, a parent suffering from psychosis can give no clear answers as to why he or she decided to kill the children, or a parent may believe killing his or her children is in the youngsters' best interest.

Yates' decision to kill her children falls in the final category, Resnick told jurors during the trial's second week. The state spent the first week laying out its criminal case against Yates through the testimony of police officers, a 911 operator and the playing of Yates' confession tape to police.

Prosecutors also showed pictures of the children's bodies and displayed the clothes they wore as each suffocated beneath the water's surface.

"This is certainly not a case of spouse revenge because Andrea Yates believed Rusty (Yates) was a good husband and a good father," Resnick testified Friday.

Since the Yates children weren't unwanted or mistreated, the only remaining possibility is that Yates killed her children for altruistic reasons, Resnick told the eight-woman, four-man jury panel hearing evidence in Yates' case.

"She was doing what she thought was right for her children," Resnick said, explaining to jurors that Yates' decision was altruistic. "She did not believe that her conduct was wrong. She believed that it was right."

Determining if Yates knew right from wrong will be a key decision jurors must make in the case where there is little debate over whether Yates drowned her children or whether she suffered from a mental illness.

To prove insanity, defense lawyers must prove Yates suffered from a severe mental disease or defect and that she didn't know her actions were wrong.

Yates faces life in prison or the death penalty if convicted.

She is charged with capital murder in the deaths of 7-year-old Noah, 5-year-old John and 6-month-old Mary. Charges could be filed later in the deaths of Paul, 3, and Luke, 2.