Less than four weeks after Toronto police Const. James Forcillo shot 18-year-old Sammy Yatim, the Ontario Special Investigations Unit has charged Forcillo with second-degree murder.

The SIU — which investigates when police officers are involved in incidents where someone has been seriously injured, dies or alleges sexual assault — acted with uncharacteristic speed in the Toronto streetcar shooting, perhaps because of videos of the incident that have been watched around the world.

Toronto lawyer Julian Falconer told CBC Radio's Mary Ito that the availability of video evidence is an important reason charges were laid when they were.

Toronto police union president Mike McCormack says Forcillo is upset about the charges, but neither he nor Forcillo was surprised. McCormack did say he's shocked that the charge is second-degree murder.

It's only the second time a Toronto police shooting has led to a second-degree murder charge. The first was in 2012 in connection with the death of Eric Osawe during a raid at an apartment in 2010, which also followed an SIU investigation. However, the judge at Const. David Cavanagh's preliminary hearing threw out the murder charge and also discharged the lesser charge of manslaughter.

Const.James Forcillo faces a rare second-degree murder charge in the death of Sammy Yatim, who was shot multiple times while apparently wielding a knife on an empty Toronto streetcar on July 27. (Movember.com/Canadian Press)

Second-degree murder implies intent to kill the victim. The Crown brings a manslaughter charge when it does not believe the killing was intentional.

Prosecuting case a "Herculean task'

Selwyn Pieters, a Toronto lawyer with considerable experience representing the families of people shot by police, told CBC News that while a charge of second-degree murder does leave the judge and jury with a number of options, including opting for a less charge, he thinks the charge in Forcillo's case should have been manslaughter.

"It's going to be a more difficult hurdle for the Crown to surmount if it's second degree," Pieters said. He described prosecuting this case as a "Herculean task."

Pieters also noted that jurors have been reluctant to convict police officers acting in the line of duty. "Rarely do we have cases where police officers are charged and heard before a jury on serious offences and a verdict of guilty is returned," he said.

Selwyn Pieters, a lawyer who has represented a number of the families of people shot by police, says the SIU should have charged Forcillo with manslaughter rather than second-degree murder. (Colin Perkel/Canadian Press)

Ross McLean, a crime specialist in Toronto, says "the SIU must feel they have compelling evidence for second-degree murder — that they feel it's warranted, that they spoke to the Crown about it and the Crown would have concurred to lay the charge, so they must feel they have a clear case."

While all the evidence that the SIU has gathered remains out of the public eye, McLean thinks they believe they can prove "there's a degree of intentionality" in the Yatim shooting.

Forcillo's defence will likely ride on self-defence arguments. Much will depend on what he says was his perception of the situation during those crucial moments early on July 27.

McLean, a former Toronto police officer, says there is a positive side to the charges: "Officers don't want to have an investigation hanging over them for months at a time. To have it come out and get dealt with right away is probably just as well for the officers."

Videos just part of the evidence

While the videos of the incident will be critical evidence, there's also the the eyewitness testimony and the other evidence, especially the pathologist's report.

Former Toronto police officer Ross McLean says thatwith the charge being laid, the case will 'get dealt with right away [which] is probably just as well for the officers.' (CBC)

That report could be as important as the video evidence, Pieters says, as it will indicate the entry and exit points of the bullets and their sequence.

Unlike many other police shootings, a number of civilians could be called to give eyewitness testimony if Forcillo is eventually tried.

While the evidence provided an objective basis for the SIU review of the officer's conduct, Pieters says coupled with that is "the public pressure, with the significant demonstrations and calls from various civil groups in Toronto for charges to be laid" that forced the SIU's hand.

In that sense, the video played a dual role, Pieters argues. Without the video, "It would have been highly unlikely that the SIU would have laid charges and it would have been unlikely that there would have been such a public display of outrage."

After noting that the SIU would say they rely on the evidence, McLean warned, "make no doubt about it, the eyes of Canada and the world are on this shooting."

YouTube videos of the shooting have been viewed about 1.8 million times and probably several times that number have seen the video on television or on other websites.

"The public is informed and they want answers," McLean said.