A young Toronto man will spend at least 10 years behind bars after been sentenced for the sexual jealousy and blackmail-driven stabbing death of teenager Stefanie Rengel.

"Death is permanent. There is no rewind button," Det. Sgt. Steve Ryan, the case's lead investigator, told reporters after the sentencing of David Bagshaw, now 19. "And as a society, we hold everybody accountable, whether you're 17 or 77."

Bagshaw, known until now as D.B. because he was 17 at the time of the crime, was sentenced Monday as an adult.

The Crown had asked an adult sentence, arguing that Bagshaw was only four days shy of his 18th birthday when he murdered Rengel -- and that his electronic communications trail showed he was well aware he would face more severe punishment if he waited much longer before striking.

First-degree murder convictions for adults over the age of 18 carry automatic life in prison sentences with no possibility of parole for 25 years.

The defence had asked for a youth sentence, arguing that adult incarceration would leave D.B. more antisocial than if he received help in a youth facility. A youth sentence would have meant six years in prison -- adjusted for time served -- and four in the community.

"As we said to the judge before the sentencing, he accepts whatever he receives," defence lawyer Heather McArthur told reporters outside court.

"And quite frankly -- right now, David is still far more concerned about the pain and the suffering he caused than he is about what's going to happen to him. And at the end of the day -- all he wants to express once again is how truly, truly sorry he is for what he did. And he knows there's nothing he can do to bring Stefanie back, but he hopes at least the family has some consolation now."

Thirteen-year-old Ian Rengel, Stefanie's brother, spoke for the family. He didn't sound satisfied with the sentence.

"Being four days shy of 18 shouldn't mean automatically knocking off 15 years off the sentence for first-degree murder. My sister Stefanie didn't even get to live 15 years. The community should be very concerned when David Bagshaw gets out in 10 years."

He added: "I don't think anyone will be able to forgive them when they get out."

In passing sentence, Justice Ian Nordheimer did say he found Bagshaw to be genuinely remorseful. He noted that two psychiatrists believed Bagshaw could be rehabilitated.

"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."

Bagshaw's former girlfriend, 17-year-old Melissa Todorovic, convinced him to kill Rengel. She was convicted of first-degree murder and sentenced in July as an adult to life in prison, with no chance of parole for seven years.

Todorovic had relentlessly pressured Bagshaw to kill Rengel, someone she had never met but for whom she harboured a pathological jealousy because Rengel once had a crush on him.

Bagshaw and Todorovic exchanged thousands of text messages and cellphone calls over a period of months, with Todorovic threatening to withhold sex until he got rid of Rengel.

He finally acted on the evening of Jan. 1, 2008, luring Rengel outside with a phone call and then stabbing her six times in the chest. A passerby found Rengel dying in a snow bank.

Bagshaw told his sentencing hearing earlier this month he can't forgive himself for killing "an innocent girl who deserved to live."

"I stand before you sentenced for the disgusting crime I committed. I hate myself for the decision I made that night. She died because of my actions," he said between tears in a statement to the court.

"To Stefanie's family: I am so sorry. To Stefanie: I am sorry."

Bagshaw will be eligible to apply for parole when he's 27. He's been given credit for the time he has already served in custody.

With a report from CTV Toronto's Chris Eby