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Nina Courtepatte's body was found on a golf course west of Edmonton in April 2005. ((CBC))

A man who was 17 when he raped and helped kill a 13-year-old Edmonton girl will serve a life sentence in prison as an adult.

Judge Janet Franklin said the crime was so "horrendous and evil" that she had no choice but to sentence Michael Williams, who turns 20 next month, as an adult.

At that point, the victim's family jumped up in the Edmonton courtroom to cheer and hug each other.

Nina Courtepatte was lured to a golf course from the West Edmonton Mall with promises of a party in April 2005. The 13-year-old was raped, strangled, stabbed and then bludgeoned to death with a hammer.

Known to his friends as "Pyro," Williams confessed to the crime as well as trying to light Courtepatte'sjeans on fire before fleeing the scene.

The judge noted Thursday that Williams suffers from mental health issues and said it may take decades before he feels any remorse.

Details of Williams's life presented in court show a troubled, destructive boy who claims to have been beaten and sexually assaulted. He saw the first of many psychologists at the age offour.

In Grade 2, he threatened to kill a classmate.

When he was 12, his mother found so many knives in his room, she refused to take care of him anymore and he was taken into custody by social services.

'Yet he didn't take the offers that was available to him to help him heal.' —Peacha Atkinson, victim's mother

Courtepatte's mother, Peacha Atkinson, says Williams's background is no excuse.

"I heard testimony in there that I couldn't even believe," she said Thursday."They did fail him in that sense but yet he didn't take the offers that was available to him to help him heal."

The defence wantedWilliams sentenced as a youth, which would have carried a maximum sentence of 10 years. Instead, the judge sentenced him as an adult for first-degree murder, which automatically means life in prison with no parole for at least 10 years.

Lawyers will have to sort out which institution will be most appropriate for Williams who was recently diagnosed as "highly psychopathic."

Five people were charged in Courtepatte's death.

Joseph Laboucan, 21, is serving a life sentence for first-degree murder while Michael Briscoe, 36, was acquitted. Briscoe had told police he was simply swept along in the events.

A 19-year-old woman was convicted of manslaughter in April, while an underage female has yet to go to trial.