TORONTO -- When Bridgette McGregor saw a knife-wielding teen lunge towards her on a Toronto streetcar three years ago, she thought he was going to kill her.

McGregor sobbed and shuddered in a courtroom on Tuesday as she recalled her encounter with Sammy Yatim for the trial of the police officer who killed the teen minutes later.

"I need people to know that Yatim was dangerous," she said. "He was going to kill me."

Const. James Forcillo has pleaded not guilty to second-degree murder and attempted murder in Yatim's July 2013 death. Court has heard that he fired nine bullets at the 18-year-old after a 50-second confrontation.

The police officer did not know what had happened to McGregor when he arrived at the streetcar, which stopped to let off panicked passengers while Yatim remained on board.

Forcillo and his partner were just told over a police radio that there was a man with a knife on the vehicle and that there had been no injuries.

Crown prosecutors argue Forcillo's actions weren't necessary or reasonable. His lawyer contends the officer's actions were justified and carried out in self-defence.

McGregor, 27, told Forcillo's trial that she was with her two older sisters and her 12-year-old niece, returning home from a Justin Bieber concert in the city, when they took seats at the back of the streetcar near Yatim.

McGregor said she first took notice of Yatim when he stretched out one of his legs in front of her but wasn't too concerned. It was only when one of her sisters, while asking aloud if it was time to get off, shifted her eyes over to Yatim's lap that McGregor noticed the teen had exposed himself.

"I didn't notice the knife at first, I only noticed he had his penis out," she said as tears flowed down her face, adding that she then became aware of a switchblade in Yatim's hand.

"He was holding a knife, masturbating."

Surveillance video from the streetcar played at the trial has shown Yatim lunged forward and swiped his knife in front of McGregor's throat before moving towards her again and standing up.

McGregor said she didn't remember the exact details of those moments, but said she recalled Yatim speaking to her.

"He tells me that I'm not going anywhere," she said. "He comes towards me with a knife and I hold up my purse."

McGregor said she also recalled feeling the thud of Yatim's knife against her purse before she managed to "scurry around" him and dash to the front of the streetcar, falling once on her way as screaming passengers rushed to the still-moving vehicle's front doors.

"I yell: 'Open the doors, why won't you open the doors, he has a knife,"' a distraught McGregor said in court, recalling that once the doors opened, she and her family rushed onto the street and began running until one of her sisters said they had to call police.

On McGregor's frantic 911 call, which was played in court, she is heard saying "he just pulled a knife on me, he attacked me," as she speaks to an operator.

McGregor started sobbing uncontrollably as the tape was played, leading Forcillo's lawyer to request a recess.

Later, under cross-examination from a Crown lawyer, McGregor said when she heard shots being fired while she was on the 911 call, she thought it was Yatim firing a gun.

Court also heard that McGregor and her family didn't tell their full story to police until after Yatim was killed.

Outside court, Yatim's mother, a fixture in the courtroom's front bench throughout the trial, said she was sorry for the McGregors, but their experience didn't compare to hers.

"I lost my son, my son killed with nine shots," said Sahar Bahadi. "I'm sorry for the ladies, but that's not related with what the police do with my son. When (Forcillo) arrived, he didn't know what happened and he shot my son in 38 seconds. Do you think that's right? I'm now going to spend Christmas and New Year with the ash of my son."

Tuesday's testimony marked the final evidence submitted at Forcillo's trial. The jury will return for closing arguments in the case in early January.