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A North Shore teenager who yesterday admitted the brutal murder of a North Shore pensioner was on bail at the time of the killing.

The 15-year-old - who cannot be named for legal reasons - pleaded guilty when he appeared in the North Shore District Youth Court.

He was remanded in custody and will be sentenced in the High Court on June 19.

But the Herald can reveal the boy was on bail - with strict curfew conditions - when he stabbed Mrs Doreen Reed to death in January.

She was found dead in her bed with stab wounds that had pierced "multiple organs", police said at the time.

The boy's bail was revoked after Mrs Reed's murder.

At an appearance after his arrest, Judge Laurence Ryan told the boy he would be held in prison because of the risk he would commit more crimes if released.

He was facing charges of fraud, car theft and burglary at the time.

Police will tell Mrs Reed's 85-year-old brother in England and 87-year-old sister in South Africa about the guilty plea.

The woman who found Mrs Reed's body - a friend of 48 years - was last night relieved the boy had "done the right thing". But she had no sympathy for the teen killer.

"It's hard to ever put into words what I feel. I just feel he has wasted his life. But then I don't know how long the sentence is going to be."

The friend said she and her husband would not attend the boy's sentencing.

"I don't want to put a face to him," she said. "He did a dreadful thing, and whatever pushed him to do it, I just don't know.

"I just hope he feels remorse."

The boy's mother yesterday told the Herald the family were horrified and struggling to come to grips with what he had done.

"He's my son, and I love him. This is not how he was brought up. It's like someone switched on a light, then turned it off."

She said her brother had been murdered about 15 years ago, and she shared the Reed family's grief and outrage.

"I know what it feels like for someone to be taken away."

She said her son was "scared and apprehensive" at the prospect of a long time in jail.

"He doesn't know why he did it ... he doesn't know what happened.

"He has blacked a lot of things out. I can't imagine what my son went through."

She said she had asked the authorities to keep her boy under observation in case he tried to do something rash.

"The only way he can see out of this is 'A life for a life, mum' ... he can't handle it."

- Additional reporting Elizabeth Binning