Ontario Ombudsman Andre Marin is launching an investigation into allegations the police Special Investigations Unit isn't doing its job properly.

Marin says there has been a "troubling" increase in the number of complaints about the SIU, the civilian agency which investigates police actions in cases involving death or serious injury.

"The allegations cannot be ignored," Marin told reporters at a press conference on Thursday.

Marin complaints the SIU is slow to investigate, isn't impartial enough and is "less than thorough'' in their investigations. Families involved have also said they aren't being given information by the agency.

"The SIU is a bulwark of democracy in Ontario,'' Marin said. "It's where the buck stops in police accountability when there is death or serious injury. Given the nature of these complaints, I believe it warrants further investigation.''

The ombudsman has received 20 complaints in the past 17 months alone, from victims, their families, lawyers and interest groups.

Marin says eight of the Toronto-area cases involving death and serious injury will be "put under the microscope'' to begin with.

Lawyer Julian Falconer, who represents several people who allege their cases weren't properly investigated by the SIU, said Marin needs to expose the culture at the agency.

"There are many good investigators at SIU but they are dominated by a pro-police culture that has reached the stage that their findings and their work can no longer be trusted," Falconer said.

"If the boil isn't lanced, it's only going to get worse.''

While he wouldn't go into detail about the specific cases involved in the review, Marin said they involved situations where police were cleared under suspicious conditions.

One case involves Hafeez Mohamed, who claims he was severely beaten by Durham Region police last year after being arrested for dangerous driving and drunk driving in Pickering.

Mohamed says he spent 42 days in the intensive care unit at St. Michael's Hospital, but the SIU didn't look into the case.

"They didn't do nothing to investigate the case or anything like that," Mohamed said.

Anne Jacot, whose 19-year-old son Nicholas Vanderboom died after a speeding motorcycle t-boned his car in October 2005, claims the SIU failed to interview two key witnesses who saw police leave the scene.

"There was a common interest in making sure there was a particular result out of (it)," Jacot said.

There are still questions about whether police were chasing the motorcycle that hit the car Vanderboom was in, she said.

Marin said he is not reinvestigating the police cases, but probing how the SIU performed their work.

The ombudsman will be looking at incidents from 2003 on and is asking anyone who has information about the SIU to come forward to his office.

Marin, the former head of the SIU, will complete the investigation by October and will make his report public by November.

SIU director James Cornish said the unit will co-operate fully with the investigation.

"I have confidence in the professionalism of the men and women of this unit and that the ombudsman will conduct an impartial and professional investigation," he said in a release.

Cornish added the SIU has been the subject of a number of reviews and audits in its 17-year history.

With a report from CTV's John Musselman and files from The Canadian Press