THE killing of a woman by her teenage foster son came out of the blue and could not have been predicted, an inquiry has heard.

Dawn McKenzie, 34, was stabbed to death in her own home after the boy been placed with her and her husband Bryan.

The boy - who was just 13 at the time - killed her in June 2011. He was jailed for seven years in 2012 after admitting culpable homicide on the grounds of diminished responsibility.

A fatal accident inquiry into her death has been told that there was nothing in the boy's past behaviour to suggest he was capable of killing someone.

Social worker Anne Ritchie, 62, published a review of the case for Glasgow City Council in 2013, said the killing had stunned social workers who had dealt with the boy.

She said: "There was nothing to indicate in his behaviour and the work done with him that he might kill someone.

"Distressed teenagers in foster care can run away, self harm, become involved in drink and drugs, steal cars, and stay out all night. He didn't do any of those things.

"I wouldn't have been surprised if he had got into trouble at school or possibly self harmed but there was nothing that would have alerted me that he might have did what he did.

"It was so beyond what might have been expected.

"There was an incident a few years before where he was threatened with a knife by a boy in the community.

"A social worker went to speak to him and his attitude was that he would never do anything like that."

Miss Ritchie, a former senior council social worker who now works independently, said the boy would never have been placed with foster carers if had shown a tendency for extreme violence.

Giving evidence, she also said she would have hesitated before placing the boy with the McKenzies as they had not fostered a child before.

She added: "I think I would have hesitated because it was their first placement.

"My concern would have been that he might have been distressed when he moved and he was becoming a teenager.

"With the issues in his background he might have been more difficult to handle.

"The teenage years can be difficult and it could have been a bad experience for Mr and Mrs McKenzie and not a good start to a career in fostering.

"But the worst thing I thought would have happened would have been that the placement had broken down. I would never have thought what did happen would happen."

Miss Ritchie had earlier told the inquiry that social workers did not take the boy into care quickly enough because they were too sympathetic towards his birth mother.

A later assessment found that the boy had suffered from the worst levels of neglect at his family home.

The boy was placed with the Mackenzies in Hamilton, Lanarkshire, in November 2010.

The inquiry had earlier heard claims he described hearing a voice in his head telling him to 'stab her'.

He told a doctor he felt a 'heatwave' of anger surge through his body after he had argued with her.

He said: "It was like butterflies you get on a rollercoaster, my head was pounding. You lose it, I have never felt such anger before.

"I was hearing voices saying 'stab her' inside my head. I couldn't control the voices.

"I felt like I was just floating above myself. I couldn't control my body, I couldn't pull myself back."

The inquiry, which is being held in Motherwell before Sheriff David Bicket, continues.