The fate of a 17-year-old Whitehorse girl accused of murder is now in the hands of youth court judge John Faulkner.

He must decide if she knew what she was doing when she fatally stabbed her mother's boyfriend early on Aug. 8, 2009.

The girl, who cannot be identified because she is a minor, pleaded guilty to manslaughter at the beginning of the trial in December, but the Crown prosecutor pursued the more serious charge of second-degree murder.

At the trial's close Friday, Gord Coffin said his client never meant to kill her 56-year-old victim, and wasn't in control of her own actions when she stabbed him 12 times in the chest and back.

It would be a mistake to think the composed, mature young woman who testified in her own defence last Thursday is the same person who committed the crime, he said.

At the time, she lacked the maturity to understand the consequences of picking up the knife, Coffin told the court. He pointed to case law which gives young killers a certain amount of leniency due to their lack of life experience.

She wanted to hurt the man, as she admitted during her testimony, but she never thought of killing him, Coffin said.

In fact, he pointed out, the psychiatrist who assessed her after the killing concluded she wasn't thinking at all as she stabbed the man.

He described her as being in a "dreamlike state” with no control of her actions.

The very fact she stabbed the man a dozen times shows she was in a "frenzy,” Coffin said, acting "without thought or intention.”

The sheer number of wounds "is consistent with an unawareness of what was going on,” he said.

Furthermore, the girl had no history of initiating violence, Coffin said. Although she was in a few school yard fights, the evidence indicates she was never the initiator, and usually she was standing up to a bully.

But prosecutor David McWhinnie refuted Coffin's depiction of his young client.

During the trial, McWhinnie called the girl's memory of the events into question, asking psychiatrist Dr. Kulwant Riar if it was possible the girl had forgotten the events of that night as a way of protecting herself. The doctor said that was possible.

McWhinnie reiterated that theory in his summary Friday, saying: "She may be innocently unreliable,” having pushed the grisly details of the attack out of her mind.

In other areas, he did not make her out to be quite so innocent. He described her as a "narcissistic and self-centred” teenager who would do anything to get rid of her mother's boyfriend.

Throughout the trial, he was described as a grumpy, sedentary, unhelpful drain on the family. He did not work and did not contribute any money to the household.

He hardly ever left his armchair in the living room, and made the girl feel like an intruder in her own home.

There was no evidence of sexual or physical abuse, although the mother described him as psychologically abusive.

But as McWhinnie pointed out, none of that is reason to be killed.

"His offence, if he committed any, was simply being,” the prosecutor said.

He also pointed out that most of the descriptions of how the man treated the girl, and how she felt about him came from other witnesses.

"Her descriptions of his conduct are not very helpful” in understanding what drove her to pick up the knife that night, McWhinnie said.

In the end, she had a "settled determination to harm someone,” and at 16 years old, she knew very well the consequences of stabbing someone.

That awareness is what makes her guilty of murder, he concluded.

Judge Faulkner reserved his decision until the end of March. Until then, the girl will continue to live with the family of an ex-police officer.

If she is found guilty of second-degree murder, the Crown may make an application to have her sentenced as an adult. In that case, she would be sentenced to life, but would be eligible for parole in seven years.

She would serve the first part of her sentence at the young offenders' facility, then be transferred to an adult facility at the age of 20.