The Supreme Court of Canada has ruled that drug evidence obtained in an illegal police search can nonetheless be used by the Crown to prosecute a Nova Scotia motorist.

In a 5-2 decision, the majority said that a Kentville man, Brendan David Aucoin, should not have been searched while an officer was preparing a traffic ticket for him.

However, they said that the need to prosecute crime outweighs the unconstitional nature of the search.

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The search arose after a routine traffic stop in 2008 by a police officer who suspected a licence plate infraction. Detecting alcohol on Mr. Aucoin's breath, the officer administered a roadside screening test and impounded his car.

Out of concern that Mr. Aucoin might disappear into a milling street crowd while his traffic ticket was being prepared, the officer asked him to get into his police cruiser.

Before opening the cruiser door, however, the officer gave Mr. Aucoin a routine pat-down search. He discovered a small package containing eight bags of cocaine and 100 green pills. Mr. Aucoin was ultimately convicted of drug offences and sentenced to two years in prison.

Writing for the majority Friday, Mr. Justice Michael Moldaver's said that the detention and search were dubious in light of the fact that other officers had been in the area and could easily have been summoned.

"Without wishing to second-guess the actions of the police and recognizing, as I do, that the police are often required to make split-second decisions in fluid and potentially dangerous situations, I am nonetheless of the view that (the officer's) actions, though carried out in good faith, were not reasonably necessary," Judge Moldaver said.

Balancing that, however, he said the sequence of events was carried out by an officer acting in good faith; not one motivated by flagrant disregard for his constitutional rights.

"As for the impact of the search on the appellant's privacy rights, I accept that the impact was significant – but no more so than society's interest in having this case tried on the merits," Judge Moldaver said, writing on behalf of Madam Justice Marie Deschamps, Madam Justice Rosalie Abella, Mr. Justice Marshall Rothstein and Madam Justice Andromache Karakatsanis.

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But in dissenting reasons, Mr. Justice Louis LeBel and Mr. Justice Morris Fish countered that the officer lacked a legitimate reason for breaching Mr. Aucoin's right to privacy.

"The Court must dissociate itself from this conduct if it is to maintain the long-term repute of the justice system," he wrote.

Judge LeBel stressed that police officers must have reasonable grounds to believe that there is a risk to their safety – or that of others – before they go ahead and conduct a protective pat-down search.

"The evidence indicated that Mr. Aucoin was cooperative throughout the encounter," Judge LeBel said. "He did not say or do anything that would indicate a desire to flee. In addition, there was a second uniformed officer present to supervise him."

Judge LeBel also noted that the officer said he routinely put detained motorists in the locked rear seat of his police car after a pat-down search.

"This is evidence of a pattern of abuse," Judge LeBel said.

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He said that admitting the evidence would condone police officers detaining and searching suspects without having any real grounds to do so: "The effect would be to significantly erode public confidence in the rule of law," he said.