A Calgary police officer who was accused of letting a friend off an impaired driving charge has been acquitted after the judge found the accused was, in fact, the victim of a "very angry" ex fiancée.

Mark McCullough was charged with obstruction of justice and breach of trust stemming from a November 2015 incident where he issued a licence suspension and had a driver's car towed.

The judge ultimately found McCullough had acted well within his discretion as a CPS officer in making the decision to proceed with a traffic charge against Caren Lileikis rather than criminally.

The charges against the officer were not laid until a year later when McCullough's ex fiancée Jessica Nelson — who also happened to be the 911 dispatcher involved in the 2015 call — went to police, said provincial court Judge Ted Fisher.

In delivering his two-hour decision, Fisher said he was "very concerned with [Nelson's] credibility, finding that she was "not an unbiased witness" and that her evidence "should be given very little weight."

After McCullough and Nelson broke up, she was angry. She had gone to police to report McCullough had assaulted her — a charge which he was acquitted of last November — and during that interview, told investigators that he had also let a female friend off an impaired driving charge.

'Full exoneration'

"Absolute joy," said defence lawyer Cory Wilson in reaction to the judge's acquittal. "Mark McCullough was wrongly accused of crimes he did not commit. Today he was fully exonerated. This wasn't a question of reasonable doubt, this was a full exoneration."

On Nov. 11, 2015, police responded to a check on welfare call for a woman who was slumped over the steering wheel of her car in a southwest parking lot.

At some point the call was reclassified to an impaired driving code but there was no evidence that change was made by McCullough or his partner.

McCullough testified the car was not running, and he couldn't see the keys. He also said there was no odour of alcohol, that he could only smell the woman's perfume.

"Mark McCullough's version of events aligns with the evidence," said Fisher in calling the accused's testimony "straight forward."

Cory Wilson says his client CPS officer Mark McCullough was "wrongly accused of crimes he did not commit." McCullough was acquitted on charged of breach of trust and obstruction of justice on Tuesday. (Meghan Grant/CBC)

Believing he did not have grounds to charge Lileikis with drunk driving, McCullough instead made the decision to suspend her licence for 24 hours and have her car impounded.

Fisher said that judgment call was well within McCullough's discretion as a police officer.

McCullough testified he realized part way through the incident that Lileikis was a witness in a minor theft investigation at a Home Depot that the officer had responded to.

He called Nelson, telling her that the Home Depot investigation was a major economics crimes case and that Lileikis was a key witness.

During the call, he said he was worried that if she was charged with impaired driving, it would affect her credibility at court as a witness.

But McCullough later testified he was just trying to impress Nelson, who was both his 911 dispatcher and fiancée.

McCullough and his partner drove Lileikis home and over the few months, they developed a friendship and eventually had a sexual encounter.

McCullough's actions 'by the book': lawyer

"It may very well be that everything was not done perfectly," said Fisher. "Imperfection, mistakes or an error in judgement do not give rise to criminal responsibility."

Prosecutor Leah Boyd declined to comment after the decision was delivered.

Wilson said the last year and a half has been "devastating" for his client.

"People are going to believe he got off on a technicality or believe got off simply because he's a police officer, and that's just not so," said Wilson.

"Everything he did was proper, by the book and according to law."