Ottawa police have turned to provincial police for assistance in their investigation of a "pattern" of violence involving the city's sex workers, CBC News has learned.

The Ontario Provincial Police criminal profiling unit is now looking at the six unsolved slayings of Ottawa sex workers dating back to 1990. They are searching for a possible link between some of the cases, which Ottawa police acknowledged in December 2011.

The provincial force's behaviour science unit is also helping the investigation by trying to eliminate and find possible suspects. This unit is also working on a profile of the potential serial predator by looking at how he operates, his fantasies, what his job could be and what he might look like.

Former RCMP profiler Glenn Woods said he believes the predator fulfilled a sexual fetish before he slayed a prostitute. He might have also left a distinct signature, which could be the link police are looking for.

"These are behaviours they want to do - but don't have to do - to commit the crime," Woods told the CBC's Judy Trinh.

"Those are the things that are most likely to link crimes because they don't change over time.

Sexual assaults widen police investigation

The slain women come from different backgrounds but many were hooked on crack cocaine and feeding their addictions by selling their bodies.

Former RCMP profiler Glenn Woods said he believes the serial predator fulfilled a sexual fetish before slaying a prostitute. (CBC)

It is still possible their deaths could lead back to one killer and to widen the investigation, police are also now looking at violent sexual assaults.

The hope, police say, is finding other victims who were abused by the killer but escaped. There is a lot of information, though, with 1,212 unsolved reported sexual assaults in Ottawa since 2001.

That has Ottawa police's major crimes unit calling in both extra officers and outside experts.

The piles of files are also the reason Ottawa police have taken so long to identify a possible link, according to the former RCMP profiler.

Social agencies and centres, such as the Minwaashin Lodge, have also been passing on information to police about possible assaults on street workers.

Former profiler calls crimes involving prostitutes challenging

But Woods said police did not ignore any "pattern" of violence or drag their feet on an ensuing investigation.

He said crimes involving prostitutes are challenging, especially those workers who live on the margins of society.

"They are high risk individuals. They place themselves at risk and make it a greater likelihood that they will be victims," Woods said.

Ottawa police do have some clues on a possible suspect, but not many.

A pair of reading glasses was found lying beside the body of Pamela Kosmack when she found dead in June 2008.

Police said the glasses look like the type a man in his 40s or 50s might use.