Update: The story below was published on Monday based on FOIP documents obtained by CBC News. On Tuesday, in response to CBC's story, ASIRT released one of those documents and elaborated on its position in relation to proffered statements.

There are concerns Calgary police are protecting officers who are under criminal investigation with "murky" and "unprincipled" practices, according to a harshly worded letter from the head of the agency that oversees Alberta police.

The Alberta Serious Incident Response Team (ASIRT) director Susan Hughson sent a letter to Calgary police Chief Roger Chaffin on Jan. 26, 2016, which was obtained by CBC News through a freedom of information (FOI) request.

In the letter, Hughson takes issue with two practices:

CPS accepting proffered statements — given on the condition it won't be held against the subject of an investigation — from officers who are under criminal investigation.

CPS disclosing evidence gathered against the subject officer to his or her lawyer while the investigation is still underway and before the Crown has decided whether to recommend charges.

"Why this would be acceptable when it would not be accepted in other cases involving subjects who are not police officers remains murky at best, and cannot be based on any articulable principle that supports accountability," said Hughson.

"I cannot imagine that it is a practice that would enhance public confidence in policing, indeed, it would only foster the perception that police protect their own and that they receive special treatment."

CPS denies protecting officers

An ASIRT report on its review of a Calgary Police Service professional standards section (PSS) investigation was also disclosed as part of the FOI request.

The documents are in relation to ASIRT's review of the PSS investigation into Cst. Stephan Baker's actions. He's the officer whose C8 assault rifle was stolen from his personal vehicle while he was off duty and parked outside a bar on April 5, 2015.

Supt. Steve Barlow, who was the commander of PSS until about a month ago, denies CPS treats officers under investigation differently than members of the public.

"Our practice with officers and with members of the public do cross over in many, many ways," said Barlow. "The practice we have in professional standards, in the end of it, is to get to the truth."

The Baker investigation was divided into two parts: the guns and gangs unit was tasked with recovering the weapon — and did so less than two weeks later — and PSS led a criminal investigation into the officer's actions.

No charges laid against Baker

PSS ultimately decided in consultation with the Crown prosecutor's office that Baker — who was already under an unrelated investigation for negligence — would not be charged criminally.

Although the guns and gangs unit was commended for its "relentless and dogged investigation" in recovering the rifle, Hughson was critical of some practices employed by PSS.

Hughson said Baker's proffered statement, which would not have been acceptable in an ASIRT investigation, impacted the Crown's decision whether to lay charges.

"The proffered or conditional statement has appeared to have obtained traction in investigations into the actions of police, particularly in Calgary," wrote Hughson. "There is no principled reason to accept these statements."

Proffered statements — statements that can't be held against the subject of an investigation — are most often given by a witness working with police and prosecutors on an immunity deal, said defence lawyer Michael Bates, who is also the vice-president and chair of the policing committee for the Criminal Defence Lawyers Association.

'Completely improper' practice

Of the hundreds of clients he's had in his nearly 15 years practicing, Bates said not one has been allowed to give a proffered statement.

"This is not an ordinary thing at all," said Bates. "It's just completely improper and it undermines any confidence that the public would have that this is a legitimate investigation."

Vice-president of the Criminal Defence Lawyers Association Michael Bates is calling on the Calgary Police Service to end the practice of treating police who are under criminal investigation differently than members of the public. (ruttanbates.com)

Baker's lawyer Willie deWit said when prosecutors are made aware an officer's version of events, they could decide — if there's no likelihood of conviction — not to lay charges, alleviating backlogs in the courts system.

"In the end, providing proffered statements to the Crown and then the investigating police agencies should lessen the cost associated with police investigations and trials and should be encouraged not only for police officers, but accused persons in general."

CPS admits disclosing evidence to cops' lawyers

Hughson said ASIRT received information that CPS was in the habit of giving officers' lawyers disclosure mid-investigation, including all witness statements, even before the officer under investigation has given his or her own statement.

"I am unaware of any other type of investigation where the fruits of the investigation are shared with the subject of that investigation before it has even concluded," wrote Hughson.

"Furthermore, I cannot imagine a more unprincipled practice that has the obvious potential outcome of tainting any statement the subject officer could provide and leaving it fraught with the possibility of tailoring to be consistent with the evidence of other witnesses."

"If what is sought is the independent recollection of the subject officer, it is difficult to comprehend how such a practice would foster this. I am confident that this information cannot be correct, however, and look forward to your response that this is not a practice followed in your service."

But CPS admits it is common practice.

Though he said it doesn't happen in every case where a police officer is under investigation, CPS is considering ending the practice of handing over disclosure to officers' lawyers mid-investigation, according to Barlow.

'End it'

"That's a practice that we have been involved in or used over the years, it is something we are currently reviewing again now if we want to continue that way," said Barlow.

No timeline has been provided by the Calgary Police Service for its review.

"What do they need to review?" asked Bates. "There's no review required."

"End it. Don't do it anymore."

Baker — whose father is also a police officer — was recently demoted after pleading guilty to misconduct under the Police Act, according to police disciplinary documents.

The officer admitted he was "well aware" of the transportation and storage policies when he ignored all CPS policies taking the rifle, along with two high-capacity magazines with ammunition, and leaving it untethered in the back seat of his car.

A CPS rifle like this one was stolen from Cst. Stephan Baker's personal vehicle in April 2015. (CBC)

At that time, the five-year officer had been assigned to desk duty for four months, facing six charges of negligence of duty for incomplete reports and evidence found in his duty bag.

CPS firearms trainer Cst. Kevin Brandner testified the gun should never be at an officer's home or in his personal vehicle.

'Facts of this case are problematic'

A final passage of Hughson's letter to the chief addressed some of the facts surrounding Baker's account of the night the gun was stolen.

"Quite frankly, the facts of this case are problematic, particularly if you have difficulty believing in the astronomical possibility of coincidence," wrote Hughson.

Though Hughson said there was an intention to be objective and fair in the investigation, she focused on the need to test Baker's account of what happened.

"It is difficult to imagine a case where it was more important for the subject officer to be challenged on his version of the events."

CBC News reached out to ASIRT to see if the organization wanted to add further comment or context to the story. A spokesperson sent a paragraph explaining the role of the investigative body that was already contained in the documents.