Woman 'blames son over tomahawk killing'

A woman on trial for murder said her 14-year-old son told her if she loved him she would go ahead with their planned killing of his father.

Prosecutor Chris Maxwell, QC, said while the 61-year-old father was asleep, the woman used a tomahawk and her son used a knife to inflict the fatal wounds.

In the NSW Supreme court on Monday, the 51-year-old woman pleaded not guilty to murder, but guilty to the manslaughter of her ex-partner in the early hours of New Year's Eve 2007.

The Maitland woman and the victim cannot be named as her co-accused is their juvenile son who has been found unfit to plead.

Mr Maxwell said the Crown did not accept her guilty plea to the lesser charge and a murder trial is proceeding before Justice Michael Grove, without a jury.

The victim was attacked in his home in Schofields in Sydney's northwest as he lay asleep.

"The accused had a tomahawk which she used to chop into the deceased a number of times in the chest and upper torso area, causing some large wounds," Mr Maxwell said.

"The young person had a knife and he stabbed the deceased a number of times."

The victim managed to get up, staggered to the front door and began to yell for help, before calling his attackers "bastards", according to the police facts.

He died from extreme blood loss before mother and son fled the scene.

They had allegedly planned the killing and visited the victim late on December 29, taking with them items including latex gloves, knives and a tomahawk purchased from Kmart.

The mother secretly spiked the victim's orange juice but he did not drink much and went to bed of his own accord, the facts said.

When she told her son she could not "go through with it", the teenager replied that if she loved him she would kill his father, the facts said.

Mr Maxwell said the woman had advanced reasons for the killing, relating to her stated belief that her ex-partner had done "bizarre and brutal" things to their son.

They included claims that he had made the boy eat his own vomit, put him in boiling hot water and covered him in shaving cream which "destroyed" his knees.

Psychiatrists concluded the woman's beliefs were "delusional" and the events had not actually happened, he said.

One psychiatrist contended that the woman had felt "compelled" to join her son in the killing so as to "protect him from further abuse".

But another referred to her having "persecutory delusions" and to the mother and son having a "pathological" relationship.

The trial will continue on Wednesday.