TORONTO - The "truly evil" act of stabbing a 14-year-old girl to death to pacify an intensely jealous girlfriend saw David Bagshaw handed an adult sentence Monday of life in prison with no chance of parole for 10 years.

Bagshaw was just four days shy of his 18th birthday when he lured Stefanie Rengel out of her Toronto home on New Year's Day 2008, stabbed her six times with a eight-inch kitchen knife and left her to die in a snowbank.

Bagshaw, now 19, pleaded guilty earlier this year to first-degree murder. Melissa Todorovic, his girlfriend at the time who is now 17, was sentenced as an adult in July to life with no chance of parole for seven years.

The two convicted murderers had a sexual relationship "marked by mutual obsession and jealousy" which culminated in Bagshaw killing Rengel after months of pressure from Todorovic, who mistakenly saw Rengel as her rival, said Justice Ian Nordheimer.

Two psychiatrists who assessed Bagshaw believe he could be rehabilitated with proper treatment, the judge noted. And by pleading guilty, Bagshaw took responsibility for his actions and spared Rengel's grief-stricken family the ordeal of another trial.

"All of those mitigating factors cannot, however, overcome the nature of David's actions - the planned and deliberate killing of a young girl, a young girl who he apparently liked and who liked him," Nordheimer told the court.

"Nor can they blind us to the fact that David still poses a threat to the safety of the public."

Nordheimer had previously described Todorovic as the "puppet master" in the murder and gave her the maximum sentence for first-degree murder committed by someone under 16 at the time of the offence.

Todorovic had been "hounding and manipulating" Bagshaw to kill Rengel for months, threatening to withhold sex, end the relationship, have sex with another boy that Bagshaw knew or kill herself unless he went through with it, the court heard.

Even though Todorovic was the "driving force in this bizarre and frightening scheme," Bagshaw never walked away from the relationship or alerted authorities to the murder plot, Nordheimer said.

"I accept that David was the more reluctant of the two partners in this evil endeavour, but that does not change the fact that he knowingly and actively participated in it," he said.

"Melissa may have given the orders but it was David who carried them out."

Bagshaw went to Rengel's home the night of the murder and lured her outside with a phone call, pretending to be one of her male friends, the court heard. She met up with him and he stabbed her, leaving her bleeding but alive on the ground.

Bagshaw went to a friend's house to dispose of the knife and hide his bloodstained jacket, then telephoned Todorovic to "report the success of his mission," Nordheimer said.

Bagshaw went to Todorovic's home, "gave her a more detailed account of this vile act and received his reward - sex," he said.

"Notwithstanding the number of times that these events have been replayed both in this court and elsewhere, they lose none of their truly evil nature when they are once again recounted," Nordheimer added.

The grisly details appeared to upset Bagshaw, who at times hunched over in his seat with his head cradled in both hands.

Bagshaw, whose identity was protected until Monday's sentencing, told the court earlier this month that he can't forgive himself for the "disgusting" crime of killing "an innocent girl who deserved to live."

Rengel's younger brother Ian said the family can move forward with their lives now that the trial process was over and Todorovic and Bagshaw's identities have been made public.

"They should pay for what they've done," he said outside court. "I don't think anyone will be able to forgive them when they get out."

Bagshaw wants people to understand he's truly "sorry for something that obviously he can never take back," said his lawyer Heather McArthur.

"David is far more concerned about the pain and the suffering that he caused, than he is with respect to what's going to happen to him," she said outside court.

"He knows that there's nothing he can do to bring Stefanie back, but he hopes that at least the family has some consolation now."

Bagshaw, an only child from a "loving home," was a poor student with a history of aggressive behaviour, including bullying younger students and frequently fighting with other boys in school, Nordheimer noted.

He was diagnosed with attention deficit hyperactivity disorder at a young age, but there were only "sporatic" efforts to address the problem and Bagshaw failed to comply with treatment or take medication, he said.

Bagshaw's history of non-compliance with treatment, coupled with the fact that neither psychiatrist could say with certainty that Bagshaw would continue treatment once he was released from prison, was a major concern in rendering a decision, Nordheimer said.

Both psychiatrists concluded that Bagshaw should not receive an adult sentence. But Nordheimer criticized their reports, saying they seem to have accepted the teen's explanations for his actions "without question" - even when the evidence appeared to contradict them - and offered explanations for Bagshaw's actions even when they provided "thin justification" for his conduct.

The Crown called for an adult sentence for Bagshaw as opposed to a youth sentence, which would have meant a maximum of six years in jail and four years in the community.

Both Todorovic and Bagshaw were dealt with "fairly but firmly" by the court, said Crown prosecutor Robin Flumerfelt.

"The more than you learn about Stefanie Rengel - and I've learned a lot - the more you realize what an incredible loss her death is, not just for her family and friends, but for this community as well," he said outside court.

Toronto police Det. Sgt. Steve Ryan, who helped lead the Rengel investigation, said he was relieved for the family.

"We got the best outcome we could have possibly received," he said outside court.