A Toronto teen accused of stabbing 14-year-old Stephanie Rengel to death admitted he killed the girl because his girlfiend threatened to commit suicide if he didn't, an acquaintance testified at the girlfriend's first-degree murder trial.

The Grade 9 student was found in the snow outside her parents' East York district home suffering from six stab wounds on New Year's Day, 2008.

The witness was 15 at the time of the allegations and can only be referred to as S.T.

During his testimony on Tuesday, S.T. told the jury the accused's boyfriend dropped by his parents' house on the evening of New Year's Day.

He said the visit was unexpected, as the boys knew each other through school, but only as acquaintances.

S.T. told the court they were in the kitchen when the boyfriend told him he'd stabbed Rengel at least five times.

The boyfriend then explained to S.T. that if he didn't kill her, his girlfriend would kill herself, the witness testified.

After that, the boyfriend's mobile phone rang. The witness told Crown prosecutor Robin Flumerfelt he remembered hearing the accused on the other end.

"She said, 'Did you do it?'" the witness said. "He said, 'Yes.'"

Accused asked for help burying jacket: witness

Under cross-examination, the witness said the accused on trial asked her boyfriend "how he was going to cover it up."

The boyfriend was nervous and told him he thought someone had recognized him, S.T. told the court. He asked the witness to help him bury his jacket.

The witness said he was feeling nervous himself and just wanted the boyfriend to leave, so he helped bury the jacket in the snow in his parents' backyard.

When the boyfriend finally left, S.T. waited to tell anyone what happened until after family guests at a New Year's dinner left.

The girl's trial continues Wednesday with defence arguments. The accused and her one-time boyfriend, who is to face a separate first-degree murder trial later this year, cannot be identified under restrictions imposed by the Youth Criminal Justice Act.