A TEENAGER who killed his foster mother heard a voice in his head telling him to "stab her", an inquiry has heard.

The boy - who was just 13 at the time - said he felt uncontrollable anger when he repeatedly knifed Dawn McKenzie, 34, in her home.

The teenager was placed with Mrs McKenzie and her husband Bryan in Hamilton, Lanarkshire, in November 2010. He 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 heard the boy was interviewed by a doctor after the killing and said he had snapped over an argument with Mrs McKenzie about his internet use and other boys he had been mixing with.

Doctor John Marshall, a forensic psychologist, said the boy told him: "She was saying who I can hang about with. I said, 'You can't chose my pals', and I thought of running away to mum's.

"She said to me, 'I'm not answering you any more.'

"I said, 'Stop no answering me.'

"I felt like giving Bryan a jab, I always feel like giving him a jab."

The inquiry heard the boy described feeling a "heatwave" of anger surge through his body when Mrs McKenzie continued to refuse to talk to him after Mr McKenzie left the house.

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."

Dr Marshall concluded the boy had suffered a temporary detachment from reality known as a dissociative state at the time of the killing.

He also said the boy had a pre-existing interest in knives and he had watched YouTube videos of gang violence

He added: "He had a heightened anger problem and struggled to tolerate boundaries and his own frustration.

"Perhaps being looked after in a foster placement away from a chaotic family backdrop might have led to an improvement but the problems remained."

Mr McKenzie had earlier told the probe if he had known more about the boy's background he would still have taken the placement but would have been "more cautious and better armed".

An expert report commissioned for the inquiry found that Mrs McKenzie's death could have been prevented if the boy had been taken into care sooner.

It said that he had been allowed to live with his birth family, where he suffered "chronic neglect", for too long.

When he was taken into care by Glasgow City Council in 2008, he was sleeping on a trampoline, had no shoes, was living in a house frequented by drug addicts and had been subjected to "frequent acts of violence".

A senior social worker at the council told the inquiry that workload pressures and structural changes within the department had distracted workers, however he denied that swifter action could have prevented the death.

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