A Quebec police officer has been charged in connection with a high-speed car crash that killed a five-year-old boy, a dramatic legal turn in a case that inflamed public opinion about police accountability.

In an about-face, Quebec's prosecutors' office announced that provincial police officer Patrick Ouellet is being charged with dangerous driving causing death in the fatal collision that killed Nicholas Thorne-Belance. Mr. Ouellet has been suspended from the Sûreté du Québec provincial force with pay.

The charge, capping a six-month independent review ordered by Quebec's Justice Minister, puts an officer on trial in a case that began with a routine drive to school by Nicholas's father in February last year.

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Mike Belance was driving Nicholas and his 10-year-old stepdaughter on Montreal's South Shore and was making a left turn on a green light when an unmarked police cruiser driving at 120 kilometres an hour in a 50-kilometre zone smashed into his grey Kia.

Nicholas, strapped into his car seat in the back, was fatally wounded and had to be extricated from the wreckage with the jaws of life. He died of his injuries in hospital four days later.

For Mr. Belance and his wife, Stephanie Thorne, the information that trickled out after their son's death compounded the tragedy. Media reports revealed the police car was not on an emergency, but a call to tail a former Liberal Party director for the province's anti-corruption squad. And the officer's black Toyota Camry had no warning lights or sirens going at the time, despite its high speed.

After an investigation by Montreal police, the Quebec prosecutor's office decided not to charge the officer.

At a press conference explaining the decision, a spokesman for the Crown appeared to blame Mr. Belance for the tragedy. He said that although Mr. Belance had a green light, it was not yet giving the priority flashing signal, so Mr. Belance was taking a risk.

The decision ignited a firestorm in Quebec, raising accusations of perceived police impunity and shaking the dead boy's parents. Ms. Thorne said her husband had done nothing wrong. "He turned. On a green light. He could never have known what was coming in front of him. I just want somebody to take responsibility," she said in a tearful interview with the CBC.

In an unusual move, Quebec Liberal Justice Minister Stéphanie Vallée named an independent committee headed by retired Court of Appeal judge Pierre Dalphond to review the evidence in the case, resulting in the decision on Tuesday.

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"The decision to lay this charge was taken independently, sheltered from all political, police or media influence," the prosecutor's office said in a statement on Tuesday.

Alexandre Cloutier, justice critic for the Opposition Parti Québécois, said the case underscores the need for the prosecutions office to be more transparent in its decisions involving police-related deaths.

"This cannot happen again in Quebec," Mr. Cloutier said. "From now on … they must at least be compelled to explain their decisions.

"This raises questions about the work of the director of penal and criminal prosecutions in general," he added.

Ms. Thorne said the start of criminal proceedings marks a new, "difficult" stage.

"We are not happy or pleased," she told Canada's public broadcaster on Tuesday. "The only thing we can ask is that we do it with a certain dignity, for my son … there will be a few answers and some clarifications about the situation. [But] it's still difficult, because my son is gone, after all."

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Mr. Ouellet is to appear in court on June 26.