A shooting death that has captured the nation's attention and sparked debate about police use of force took a dramatic turn Monday, when the Toronto officer involved in Sammy Yatim's killing was charged with second-degree murder and the victim's family issued its most critical statement yet.

Constable James Forcillo, a married father of two and a police officer for six years, is just the third officer to be charged with murder in Ontario since the province's Special Investigations Unit was launched in 1990, and he is the second Toronto officer to face such a charge.

The unit, which investigates civilian deaths and serious injuries involving officers, announced Monday it has "reasonable grounds" to believe Constable Forcillo committed a crime in the killing of Mr. Yatim.

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The 18-year-old was alone on a streetcar and wielding a knife when police fired nine shots at him, then tasered him just after midnight July 27.

Mr. Yatim's family, including his parents and his 16-year-old sister, Sarah, had until Monday emphasized their trust in the Canadian justice system and said they bore "no ill will" toward Toronto police officers generally.

But in a strongly worded statement released hours after the charge was announced, the family members described their hope that the SIU will also review the actions of the 22 witness officers "for their lack of intervention in this tragedy."

"Over 20 uniformed police officers were present and no one stepped forward to stop the gun shots or offer any mediation," said the statement, which also announced the family has retained Ed Upenieks, a lawyer from a firm in Brampton, Ont.

The president of the Toronto Police Association, Mike McCormack, expressed disappointment at the charge and said the family's view is conjecture based on what they have seen online. "That's their observation from media reports, from YouTube, whatever, the Internet, that's not really talking about what happened," Mr. McCormack said, adding that he offers his condolences.

The case has riveted Toronto, which has seen two protest marches and a vigil as citizens publicly debate what constitutes appropriate use of force against the emotionally disturbed. It has prompted three probes – by the SIU, the Ontario Ombudsman and Toronto police, which last week appointed retired judge Dennis O'Connor for a mandated internal review of police practices.

According to witnesses aboard the streetcar, Mr. Yatim brandished a three-inch knife, and then passengers and the driver fled to safety. Cellphone videos and surveillance footage captured what happened next – a verbal exchange with police, three gunshots ringing out before Mr. Yatim drops to the streetcar floor, another six shots, and then the buzzing of an officer's taser.

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The officer who used the taser – a controversial police tool catapulted into the headlines in 2007, when Robert Dziekanski died after being tasered repeatedly at the Vancouver airport – was not investigated by the SIU because it determined only one officer contributed to the death of Mr. Yatim, who died in hospital. Constable Forcillo called out for a taser before opening fire, according to a source.

Toronto Constable David Cavanagh was charged with murder in the 2010 death of a Nigerian-born father during a struggle. However, that case is different because of questions over whether his gun was accidentally fired. The charge was upgraded from manslaughter to second-degree murder but then dismissed, with the Crown subsequently arguing to reinstate the original charge. Unlike that incident, the Yatim shooting was captured on video and widely circulated online.

Toronto Police Services referred all questions on the Forcillo case to the SIU on Monday. The force's court services division provided no comment about Constable Forcillo, a former court security officer.

The SIU would say nothing beyond what was in its sparsely detailed statement, citing judicial due process as the reason it cannot explain why it chose second-degree murder over manslaughter or what constituted "reasonable grounds." (Manslaughter is a homicide committed without intention to cause death, while second-degree murder suggests a deliberate, though unplanned, killing.)

And while Alok Mukherjee, chair of the Toronto Police Services Board, said the board "recognizes this is a difficult time for all parties involved," he added that the facts would come to light in court and that he would not comment further.

Constable Forcillo's lawyer, Peter Brauti, said his client will make an appearance on Tuesday at 9 a.m. after surrendering into SIU custody. A bail hearing, which Mr. Brauti said he hopes will be "as soon as possible," will be scheduled at Old City Hall at that time.

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With reports from Vidya Kauri, Daniel Bitonti and Oliver Moore