In late 2014, then-Montreal Mayor Denis Coderre picked up the phone to grouse at the city's police chief.

A journalist had inquired about a traffic ticket that had allegedly been made to go away. Mr. Coderre's angry response – the ticket had been paid, and he smelled a smear campaign by restive police union members – ultimately led to a independent public inquiry.

Now, Justice Jacques Chamberland of the Quebec Court of Appeal has reported back and issued 27 recommendations that range from informing news organizations when warrants are sought to the improvement of investigative methods and training.

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More crucially, Justice Chamberland is of the view police should be legally insulated from any interaction that can be perceived as political interference. Provincial law should be updated to give them the power to, in effect, hang up the phone without fear or favour.

That's an excellent idea, and it could easily apply beyond Quebec. So can others to create more distance between cops and politicians, like protocols for documenting exchanges between police and elected officials when it comes to investigating media outlets, instituting arm's-length hiring processes for police department heads, and codifying legislators' transparency obligations.

None of those measures are practicable without clear lines of authority and independent civilian oversight of policing; Ontario recently revamped its structures in that regard. Other places, including Quebec, lag far behind.

Justice Chamberland found no wrongdoing on Mr. Coderre's part. But a short time after his call, detectives searched the phone records of the journalist who made the initial inquiry, La Presse columnist Patrick Lagacé.

When L'affaire Lagacé burst into public view two years later, a series of similar revelations followed. They concerned scores of reporters, indicating a systematic pattern of police over-reach.

As a result, Parliament recently enacted a law expanding the protection of journalistic sources.

That's a good start – and thanks to Justice Chamberland's serious, comprehensive report, we have a clear map for what should come next.