CBC News has learned that an off-duty detective in the Ottawa Police Service's drug unit took an unmarked police vehicle to Montreal to attend a colleague's bachelor party.

The incident occurred on Saturday, March 25, and is only coming to light because the officer was pulled over by Montreal police that afternoon.

Montreal police will not say why the unmarked vehicle appeared on their radar, but do say that no charges were laid against the officer.

CBC News sought comment from the drug unit, but none of the supervising officers responded to questions.

OPS 'aware of an incident'

Instead, the force's media relations department issued this statement: "We are aware of an incident involving the unauthorized use of an Ottawa Police vehicle. The matter has been investigated and dealt with through an internal discipline process."

CBC is not naming the officer because he hasn't been charged. Multiple sources within the force tell CBC that the detective told Montreal police he was surveilling a target in that city — even though he was off duty at the time.

Sources said the constable did not have his OPS badge with him, and instead referred to his police-issue handgun as proof of his law enforcement credentials.

While it is standard practice for undercover officers to store their gun in a lock box in their unmarked vehicles, officers are not supposed to have a gun with them when they are off duty.

This is the type of institutional behaviour that sows mistrust in the police. Michael Spratt , Ottawa defence lawyer

Sources also told CBC News the officer is banned for one month from driving the unmarked vehicle assigned to him. However, the case hasn't been sent to the police service's professional standards section, which investigates potential code-of-conduct violations under the Police Services Act.

Officers who are charged under the act must face their offenses in public hearings.

Eli El-Chantiry, chair of the Ottawa Police Services Board, said he wasn't aware of the incident — which occurred three weeks ago — until CBC told him about it.

El-Chantiry said there are clear rules stating that police vehicles aren't to be used for personal purposes. Authorization must be obtained for officers to drive vehicles out of town or to take them home, he said.

'Sows mistrust'

The lack of transparency concerns criminal defense lawyer Michael Spratt.

"This is the type of institutional behaviour that sows mistrust in the police. This isn't a teenager that stole his parent's car and gets grounded," Spratt said.

Ottawa lawyer Michael Spratt is urging the police force's professional standards section to investigate the officer's actions. (Hillary Johnstone/CBC)

The effectiveness of police testimony is built on their credibility as a "truth teller," he added.

"It's the lie that's worse than the lapse in judgement," Spratt said. "You and I don't have the power to use force or to present information that can incarcerate people."

Spratt pointed out that he's represented clients who have been charged with obstruction for lying to police. He urged Ottawa police to investigate the matter through their professional standards section and delve deeper to see if the incident reflects a pattern of behaviour.

"It needs to be aired," he said. "Light and transparency is the best disinfectant to questions about institutional professionalism."