While a nearly eight-month investigation by Ontario's police watchdog has led to charges against an Ottawa police officer, the odds are stacked heavily against a conviction, if the record is any indication.

Since 1990 — when the independent Special Investigations Unit was created to look into cases of death, serious injury or sexual assault involving police in the province — a total of 15 police officers in Ottawa have had charges laid against them.

None resulted in a conviction.

Ottawa police Const. Daniel Montsion is facing a charge of manslaughter in the July 2016 death of Abdirahman Abdi. (Still from YouTube video)

Ottawa police Const. Daniel Montsion is now facing charges of manslaughter, aggravated assault and assault with a weapon in the death of Abdirahman Abdi last year.

Abdi lost vital signs during a confrontation with Montsion and Const. Dave Weir outside Abdi's apartment building in Hintonburg on Sunday, July 24, 2016.

Weir was deemed to have been a witness officer in the case and is not facing charges.

Ottawa officer acquitted in 1993

In Ottawa, Montsion is the second officer ever charged with manslaughter following an SIU investigation.

The first charge followed the 1991 shooting of Vincent Gardner during a botched drug raid. Ottawa police officer John Monette said he had mistaken Gardner's guitar for a gun.

Monette was acquitted in 1993.

The shooting of Vincent Gardner during a botched raid in 1991 led to a manslaughter charge against Ottawa police officer John Monette, who was later acquitted. (CBC)

Across the province, 19 officers have been charged with "culpable homicide," such as manslaughter or murder, since the SIU came into existence.

One was convicted.

The low number of charges and low conviction record have contributed to calls for more accountability from the oversight bodies that investigate police.

The recommendations from a province-wide police oversight review led by Justice Michael Tulloch is due at the end of March.

Former SIU director says more changes needed

​The SIU's former director, who served from 2008 to 2013, said he thinks the zero conviction rate in Ottawa is an anomaly, but conceded that making charges stick is challenging.

Ian Scott, who was the SIU's director from 2008 to 2013, says he believes Ottawa's zero conviction rate is an 'anomaly.' (CBC)

"Police are in a very unusual circumstance when criminal charges are laid against them," Ian Scott said, explaining that it's more complex because officers are tasked by society to use force if necessary.

Police also have "very good lawyers," and often juries are sympathetic to the challenges officers face, Scott said.

Until it was struck down by a Supreme Court decision in 2013, witness officers, for instance, were allowed to confer with police union lawyers before writing up their notes. And unlike most witnesses to a crime, police witnesses have their lawyers present when they give their statements.

"I think there's still room for improvement," said Scott, adding that the SIU is under increasing public pressure to be more transparent, especially when victims from marginalized communities are involved.

The increasing availability of video evidence from bystanders has also increased public judgment of police behaviour.

Scott was the SIU's director for five years until 2013, and he brought forward the charges against Toronto police officer James Forcillo — including second-degree murder — in the death of Sammy Yatim on a street car.

The shooting death, which was captured on cellphone video from multiple angles, led to protests and calls for accountability.

Matt Skof, president of the Ottawa Police Association, says the SIU's investigations are motivated by politics. (CBC)

In the end, Forcillo was convicted last summer of the lesser charge of attempted murder and is now appealing a six-year sentence, one of the harshest laid to date against a police officer.

Police union says SIU motivated by politics

Matt Skof, president of the Ottawa Police Association, said he thinks the decision to charge officers is motivated more by public pressure and politics, and that using the criminal justice system costs taxpayers millions of dollars.

The conviction record should be a strong sign that perhaps other means should be used to discipline officers, he said.

The shooting death of Sammy Yatim led to a rare conviction of Toronto Police officer James Forcillo. (CBC)

"In the last three years, the officers haven't even been reassigned from their [jobs], and rightfully so, because these charges are completely inappropriate," he added.

In Montsion's case, he was reassigned to a desk job until Monday's charges were laid and he was suspended with pay.

Public seeks more SIU transparency

A member of COMPAC, the Community and Police Action Committee, said the conviction rate is a problem if the opaque nature of SIU investigations continues.

"It is a concern when you look at the numbers and the stats," said Ketcia Peters, who has voiced concern about the length and transparency of SIU investigations and has spearheaded efforts to get SIU officials to explain its process to the public.

"If we know exactly what took place so we can understand better how those results and decisions were made, then it would help the community better understand those stats."