The younger brother of murdered teen Stefanie Rengel told a Toronto courtroom on Monday that he blames himself for not hearing his 14-year-old sister cry for help as she lay dying on a snowy sidewalk outside their East York home.

The boy read out his victim impact statement at a sentencing hearing for the teenaged girl convicted of masterminding his sister's murder.

The sentencing hearing for the convicted teen, known publicly as M.T., was supposed to begin in May, but was delayed until this week.

During Monday's proceedings, the court also heard from Rengel's grandmother and her mother who tearfully described how she has wanted to stab herself to feel the pain that her young daughter endured.

"I have wanted so many times to not be alive," said Rengel's mother Patricia Hung. "I have an incomprehensible need to feel her pain but we have other children and other responsibilities so I go on."

Rengel died on New Year's Day in 2008, when she was fatally stabbed outside her home.

"Why didn't I look out and see her dying in the snow?" said Rengel's 13-year-old brother Ian. "I could have told her I loved her and that everything was going to be fine if she could just hold on for a while longer."

M.T. , who is now 17 years old, was convicted of first-degree murder on March 20, after a trial revealed the details of her desire to see Rengel dead. The Crown is arguing the girl should receive an adult sentence for her crime.

Hung looked directly at M.T. and said she can't forgive her.

"I want inner peace, which is believed to come from forgiveness but I am unable to forgive someone who has shown no remorse.

"Knowing that I did not do enough to protect Stefanie from these monsters eats at my sanity every waking moment," she said.

'Coldness frightening'

During M.T.'s trial, the jury heard how she pressured her boyfriend, publicly known as D.B., to kill Rengel for several months. For months, M.T. threatened to break up with her boyfriend and to withhold sexual favours from him, unless he killed Rengel.

The Crown alleged that M.T. was highly jealous of Rengel, who once had a short relationship with her boyfriend.

"She asked (D.B.) to re-enact the crime, then have a little sex and then call her mummy for a celebratory latte," Hung said. "This is the most revealing glimpse into who she is and the danger she poses.

Rengel was lured outside of her home by a phone call on the day that she died. D.B. stabbed her six times and fled the scene on foot.

A passerby found Rengel struggling at the side of the road. He asked her who had stabbed her, and she said a name that sounded like D.B.

In April, 19-year-old D.B. pleaded guilty to first-degree murder and admitted to killing Rengel. His sentencing hearing is scheduled for September.

In her victim impact statement, Rengel's maternal grandmother addressed M.T.

"She has managed somehow to reach the age of 17 without the slightest regard for the intrinsic value of human life," said Mary Fraser.

"Her coldness is frightening," she continued to say. "More so because she represents a growing number in the insular world of today's youth who learn quickly from the cradle that the young are seldom required to suffer the consequences of their actions."

If M.T. is sentenced as an adult, she faces a minimum of 25 years in jail. If she is sentenced as a youth, she will face six years in jail plus 4 years of community supervision.

The sentencing hearing continues this week with the testimony of psychiatrists who evaluated the convicted teen.

With files from CTV Toronto's Chris Eby and The Canadian Press