A sniffling, crying D.B. read from a handwritten note and told the family of Stefanie Rengel how sorry he was for having stabbed her to death outside her home.

"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," the 19-year-old said Thursday in court.

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

Patricia Hung, Stefanie's mother and a Toronto police officer, bowed her head and wiped away a tear.

D.B. attacked Rengel, who once had a brief crush on him, on the evening of Jan. 1, 2008. He lured her outside with a telephone call and plunged a knife into her six times.

He did so at the behest of his girlfriend, 17-year-old Melissa Todorovic, who denied him sexual access unless he killed her perceived rival.

A jury convicted Todorovic of first-degree murder on March 20. On July 28, Justice Ian Nordheimer sentenced her as an adult to a term of life in prison with no possibility of parole for seven years.

He will soon have to weigh whether or not to do the same with D.B., who pleaded guilty to first-degree murder on April 9, who cannot be named unless he is sentenced as an adult.

Crown prosecutor Robin Flumerfelt urged Nordheimer to go with an adult sentence, saying the offender was only four days shy of his 18th birthday when he murdered Rengel.

"Had he waited four days, we wouldn't be here, his penalty would have been automatic - life in prison - with no chance of parole for 25 years," said Flumerfelt.

If D.B. is sentenced as a young offender, he would serve six years in closed custody and four more in open custody. Flummerfelt said a youth sentence would leave D.B. completely unsupervised by the age of 28.

He described D.B.'s act as a "planned and deliberate killing ... he was stalking her like prey."

Defence lawyer Heather McArthur argued her client had spent months trying to fend off Todorovic's demands that he kill Rengel.

A defence-commissioned psychiatrist described teen murderer D.B. as "functionally retarded" in his emotional development.

In his presentation to the court, Dr. Derek Pallandi said he thinks Stefanie Rengel's killer would be best put in a youth facility rather than sentenced as an adult.

Because D.B. has an underdeveloped sense of self, he's at risk of becoming more antisocial if sentenced to serve a term in an adult prison, he said.

A Crown-commissioned psychiatrist has put D.B. at a moderate risk of reoffending in the next decade.

The hearing is to continue on Friday.

With a report from CTV Toronto's John Musselman