Her eyes were wider than what I'd consider normal

David Knapp, first police officer on scene

As her trial got underway in Houston, defence lawyer George Parnham said his client suffered from post natal depression with psychotic features, which he described as "the cruellest and most severe of mental illnesses".

Prosecutors agreed that she suffered from a mental illness but said that Mrs Yates was well aware of her actions when the children were killed last June.

"She knew this was an illegal thing. It was a sin. She knew it was wrong," Harris County Assistant District Attorney Joe Owmby said.

Support from husband

Her husband, Russell Yates, has said he stands by his wife, saying she had twice attempted suicide and had been in and out of psychiatric hospitals for treatment.

Yates' children had been drowned in a bathtub in the family's home

The children, aged between six months and seven years old, were found dead in the family home in June last year after Mrs Yates called the police.

Four of the children were discovered under sheets on a bed while a fifth was found in a bathtub. All had been drowned.

Mrs Yates fidgeted and pulled at her fingers as she sat through the testimony of the first witness, police officer David Knapp, who was the first to arrive at the Yates' home after the killings.

No emotion

Mr Knapp said that when Mrs Yates opened the door to her house her hair and her clothes were wet.

She told him that she had called the police because she had killed her children. He said that she led him to the master bedroom where four of the children lay.

If she [had] received the medical treatment that she deserved, then the kids would be alive and well

Husband Russell Yates

According to Mr Knapp, "her eyes were wider than what I'd consider normal", but other than that, he said, Mrs Yates had displayed no emotion.

Jurors heard Mrs Yates' emergency call in which she requested police and an ambulance and told the switchboard operator she was "ill".

History of depression

Mrs Yates' medical records reportedly give full details of her frequent bouts of depression and suicidal behaviour.

And a doctor also reportedly cautioned Mrs Yates and her husband not to have further children following the birth of their fourth child.

Yates' husband says he is standing by his wife

She may face the death penalty under Texas law, which states that the murder of a child under six or the killing of two people at the same time warrants capital punishment.

The case has strongly divided American opinion, with many unnerved by the prospect of sending a woman to the execution chamber but outraged by the horrific nature of the crime.

Denied treatment

Others, particularly women's rights groups, have argued that Mrs Yates had been denied treatment she desperately needed and should now be helped, not punished.

Mrs Yates' husband echoed this sentiment when in a January interview with American television station CBS he said the blame for his children's death lay with the doctors who he claimed failed to treat her successfully.

"I don't blame her a bit," he said on the station's 60 Minutes programme.

"If she [had] received the medical treatment that she deserved, then the kids would be alive and well. And Andrea would be well on her way to recovery."