Rene Verret confirmed at a news conference no charges will be laid against the provincial police officer, whose cruiser hit the man's vehicle at 108 km-h — twice the speed limit of 50 km-h where the accident occurred last February.
"In criminal law, the burden of proof that the Crown has to meet is important because it has to demonstrate the guilt of the accused beyond a reasonable doubt," Verret said.
"In light of the evidence, applicable law and jurisprudence, the (prosecutor's office) is not morally convinced it can establish...that the conduct of the police officer in these circumstances represents a marked deviation from the standard of reasonable diligence and thus obtain a conviction."
The officer's vehicle was the middle of three unmarked cruisers that were tailing another car in a surveillance operation that reportedly targeted a former director of the Quebec Liberal party.
The prosecutor's office said the other motorist, who was driving a Kia, entered the intersection without having full priority in what it described as "a manoeuvre not without risk."
It added that a traffic-accident expert concluded that the cruiser was going up to 122 km-h before it began slowing down 60 metres from the intersection. It was 38 metres from the car when the motorist entered the intersection.
"In a statement at the time of the accident, the driver of the Kia acknowledged having noticed that the vehicle coming in the other direction was going at a high speed," Verret said.
"As he (the Kia driver) turned, the light had been green for a while. He said he travels in the area every day and knows that there is a priority for turning left — that is a flashing light. He added he should have waited for this priority and not tried to turn at the moment he did."
Verret noted that officers involved in such surveillance operations are authorized to exceed the speed limit if circumstances warrant it.
"They are trained for this type of behaviour and their (cruisers) are considered emergency vehicles."
Verret said the Crown concluded that the officer was doing "important" work and that it was "necessary" for him to go at a certain speed.
"The prosecutor didn't have to have all the information," he said. "For him, it was important to know, to consider, that the police officer, with the work he had to do, had to go beyond limits."
The Crown had been widely criticized for not meeting with the family of the boy, who died four days after the accident. Verret confirmed that a meeting took place Friday.
In Quebec, there is no special investigations unit or separate body to look into such accidents. Rather, a force from another jurisdiction — in this case the Montreal police — investigates and submits a report to the Crown, which decides on charges.
Montreal La Presse, quoting police documents, said the cruisers in the surveillance operation were targeting Robert Parent, who was director of the Quebec Liberal party between 2003 and 2008, in an anti-corruption probe involving businessmen, elected officials and civil servants.
La Presse reported that Parent told the newspaper he met three times with members of Quebec's anti-corruption unit.
"They wanted to know how the party works and what its administrative procedures are," the newspaper reported Parent as saying. "It was very technical."
Premier Philippe Couillard was asked about the controversy on Friday.
"Our chief prosecutor is a totally independent institution who should always remain independent from any pressure from the media or from politicians," he told reporters in Toronto where the Quebec and Ontario cabinets were holding a joint meeting.