Richard Colvin, a former senior diplomat with Canada's mission in Afghanistan, testifying before a parliamentary committee on Nov. 18. (Sean Kilpatrick/Canadian Press)

Canada's military police have been quietly investigating allegations for more than a year that the country's troops abused Afghan detainees, CBC News has learned.

Canadian soldiers captured the detainees sometime in 2008 and the investigation into their conduct has been ongoing for at least a year.

It was uncovered in documents obtained by CBC News. The documents were written for Defence Minister Peter MacKay in March to prepare him for question period.

The documents reveal that in 2008, military police launched six separate investigations into allegations of abuse involving Canadian troops.

"The military police determined that the allegations were unfounded in five of the six cases, and the remaining investigation is ongoing," said Maj. Paule Poulin, a spokesperson for the Canadian Forces Provost Marshall.

For more than a month Parliament has been seized with questions about the treatment of detainees in Afghan hands.

It started when Richard Colvin, a former senior diplomat with Canada's mission in Afghanistan, claimed that all detainees transferred by Canadians to Afghan prisons were likely tortured by Afghan officials.

"According to our information, the likelihood is that all the Afghans we handed over were tortured," Colvin told a parliamentary committee on Nov. 18.

The government's response to opposition questions about Colvin's testimony was to accuse opponents of smearing the good name of Canadian troops.

"The member is suggesting by implication that the military did something wrong, that somehow they did not do the right thing. That is what is so despicable," MacKay said on Dec. 10.

However, MacKay apparently never told the House there were allegations against Canadian troops, at least one of which is still being investigated.

That is in addition to the ongoing court martial of a Canadian captain charged earlier this year with murdering a wounded Afghan fighter in his custody.