Police being investigated after a shooting should not be allowed to talk to a lawyer before preparing their notes, the Supreme Court of Canada has ruled, in a strong rebuke to a common practice of Ontario officers.

The ruling on Thursday has wide implications because the court said protecting public confidence in the police is so vital that government can limit police rights, even to basic legal advice.

"So long as police officers choose to wear the badge, they must comply with their duties and responsibilities . . . even if this means at times having to forego liberties they would otherwise enjoy as ordinary citizens," Justice Michael Moldaver wrote.

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Douglas Minty, a 59-year-old developmentally disabled man, and Levi Schaeffer, a 32-year-old with psychiatric problems, were shot dead by Ontario Provincial Police officers in separate incidents in 2009. Both were armed with a knife. In both cases, supervising officers told the officers under investigation to consult with lawyers before preparing their notes. Those same lawyers represented other police officers who witnessed the incidents, and the lawyers had a legal duty to share the notes with all of their clients.

The court said unanimously that lawyers could not approve a draft of police notes because to do so would undermine public confidence in the investigations. Ontario created the country's first civilian body, the Special Investigations Unit, to move away from the biased appearance of "police investigating police."

Justice Moldaver deplored the process that police followed after the shooting of Mr. Schaeffer.

"Both officers completed their notes only after their lawyer had reviewed their draft notes. Neither officer ever provided their original draft notes." As a result of the lawyer's involvement, the SIU concluded it did not know what happened in the shooting, Justice Moldaver wrote. "Surely this is not the stuff out of which public confidence is built."

Police expressed disappointment but said they would comply with the ruling. "An SIU investigation is a criminal investigation, and anyone else who is faced with a criminal investigation has that right to seek guidance from counsel. That's why we're disappointed," Dan Axford, interim president of the Police Association of Ontario, said.

Justice Moldaver, an Ontario judge appointed to the court by Stephen Harper, is often viewed as helping move the court to a more pro-police position on crime.

Three judges, including Justice Morris Fish, who heard the case before his retirement in the summer, would have allowed police to consult with a lawyer before the notes were prepared, but only in a limited way. Justice Fish was considered the court's strongest voice for accused rights.