HOUSTON -- The psychiatrist who cared for Andrea Pia Yates at the time she confessed to drowning her five children testified in her capital murder trial Monday.

Dr. Muhammad Saeed was grilled by the defense about the care he gave Yates while she was hospitalized twice at Devereux Texas Treatment Network, a psychiatric facility.

Defense attorney George Parnham questioned many aspects of Saeed's care, asking about the doctor's observations of Yates, his diagnosis of her illness and the medications he prescribed.

Two days after Yates' last appointment with Saeed, she drowned her children.

Parnham asked Saeed why he didn't consult with Yates' previous psychiatrist immediately after she was admitted. He also prescribed a different medication than her earlier doctors.

Parnham also wanted to know about discrepancies between the doctor and nurse's notes, pointing out that Saeed wrote that Yates was eating solid food the same day that the nurse said she refused everything but liquids.

Saeed was also asked why Yates, who has no history of drug or alcohol abuse, was put into group drug therapy classes, suggesting that Devereux needed more clients to meet certification requirements.

Parnham asked, "How many heads do you have to have in a room together with folks with heroine needles in their arms?"

Defense expert witness Dr. Ellen Allbritton took the stand shortly after the trial began at 10:30 a.m. Monday at the Harris County Courthouse in downtown.

Allbritton was the doctor who admitted Yates into the Devereux Texas Treatment Network in March 2001, before the children's drownings.

Allbritton testified that Yates and her husband were both reluctant to admit her into the hospital.

When she was admitted, Allbrittton said that Yates was in a "catatonic state."

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

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

Defense lawyers say she is not guilty 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.

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.

The defense could wrap up its case as early as Tuesday, after more medical experts are called to testify, as well as Andrea Yates' mother.

Once the defense rests, prosecutors will call witnesses to refute defense testimony.

The jury could get the case on Monday.