The Toronto police officer charged in the shooting death of Sammy Yatim on a downtown streetcar in 2013 told a Toronto court today that the 18-year-old left him with no option but to shoot him on the night of his death.

"If I had done nothing, he would have stabbed me," Const. James Forcillo said at his trial, being held in front of a jury in Ontario Superior Court. "If I had waited for the Taser, he would have been off the streetcar. He forced my hand. He was the one who decided to come forward."

The 32-year-old has pleaded not guilty to second-degree murder and attempted murder in the July 25, 2013, fatal shooting of Yatim, who was holding a knife on the empty 505 Dundas streetcar when police arrived on the scene. Passengers and the driver had fled the public transit vehicle after Yatim exposed himself, caused a disturbance and brandished a knife aboard the streetcar.

"Mr. Yatim got shot because he came forward. He's responsible for his actions," Forcillo said.

An autopsy determined Yatim was hit with eight bullets on the night he died. In earlier testimony, Forcillo admitted to firing three shots at the teen, pausing, then firing six more after the teen hit the ground.

Video of the incident shows Yatim dropping to the floor of the streetcar after the first three shots, and making no attempt to get up off the floor.

Forcillo denied shooting the teenager on a mere hunch that he was getting off the streetcar with a knife. Instead, he insisted Yatim was coming off the streetcar and posed a threat. That's why the officer insisted Tuesday that he used the correct use of force in dealing with the teen.

"Yatim was advancing towards me," the police officer said Tuesday.

After the teen was shot, Forcillo testified, he looked like he was re-arming himself and was in the process of getting up.

Last Thursday, Forcillo said no one was more shocked than he was to see on video that Yatim didn't attempt to get up after going down after the first volley of gunshots.

Were there other options?

The officer has spent three days in the witness box, with his lawyers focusing on the training he received. Forcillo testified he applied what he learned when he fired his gun. He also maintained he was acting in self-defence.

But Crown prosecutor Milan Rupic, who has spent two days cross-examining Forcillo, has suggested that the officer lost his cool and used excessive force while dealing with Yatim.

Rupic said Forcillo didn't consider any options aside from force. He asked why Forcillo did not use pepper spray on the night of the incident, to which the officer replied it was not the right thing to do under the circumstances.

Forcillo's testimony is unlikely to extend past today as the cross-examination has already ended. It's unclear who the defence will call next to testify.

The judge said Tuesday he expects the case to conclude on Dec. 18, with final procedures slated for early January 2016.