Linda Bush, mother of a man who died in RCMP custody, supports a private members bill to force a change in investigations of police. (CBC)

A civilian watchdog agency would investigate deaths or serious injuries that occur to people in RCMP custody, under a private member's bill introduced Monday in Parliament.

New Democratic MP Nathan Cullen said the creation of his proposed civilian investigation service would end the practice of having the RCMP investigate its own members.

Family members of Ian Bush, who died in RCMP custody in 2005, joined Cullen on Monday to help publicize the bill.

Bush, 22, was taken into RCMP custody for a minor offence in Houston, B.C. Hours after Bush arrived at the police detachment, Const. Paul Koester killed him with a shot in the back of the head.

The officer claimed self-defence, and RCMP investigators found no wrongdoing on his part.

Bush's mother said today that the RCMP investigation was inadequate.

"I think that it's impossible not to have a bias when they are investigating themselves," Linda Bush said in an interview on CBC TV's Power & Politics.

"I think that even if it was a different police force, it's still police, and they're still going to feel an affinity towards the officer who caused the death."

'Trust in Mounties eroded'

Cullen said public trust in the Mounties has eroded because of incidents in recent years, and his bill would help rebuild confidence in the force.

Bush said things would have to change before her confidence in the RCMP could be restored.

Ian Bush was shot to death while in police custody in Houston, B.C., in 2005. (CBC)

"I'm a Canadian who was always very proud of the RCMP and I think it's a real shame that Canadians can't be proud of their icon anymore," she said.

RCMP Commissioner William Elliott has said that the RCMP should no longer investigate incidents of deaths or injuries to people in their custody and that the force is seeking more transparency in investigations into its own members.

Private member's bills rarely become law, but Cullen said he thinks this could be an exception.

"I think we can have a real chance at having a bipartisan effort here on the Hill to do something," he said.

The government has said it is looking at RCMP reforms but first it wants to see the report of the Air India inquiry, which is expected soon.

With files from The Canadian Press