A Taliban fighter captured by Canadians last summer vanished within hours of being released to Afghan authorities, military documents reveal.

Obtained under Access to Information legislation by The Globe and Mail, the documents highlight the holes in a controversial prisoner handover agreement signed between Canada and Afghanistan in 2005.

Canadian soldiers captured Taliban fighters during and after a battle last July in the Panjwaii district of Kandahar province.

Four of the detainees were taken to the Kandahar Air Field (KAF) for questioning and another died of his wounds while in Canadian custody.

A sixth prisoner vanished after Canadian troops handed him, and two others, over to the Afghan National Army (ANA).

It is unclear what happened to the man. However, a situation report by a Canadian military captain says "the ANA had lost contact with one of the detainees."

The man could have escaped, bribed his way out or have been killed by the Afghan guards, The Globe reported.

"What's very unclear at the moment is what really are the rules for the soldiers out there," CTV's Paul Workman reported from Afghanistan.

"We're told that prisoners taken are supposed to be interviewed in the field once, and then interviewed again back at the Kandahar Airbase before they're passed on to Afghan authorities.

"It seems that this man ... was taken prisoner and handed over in the battlefield itself."

The report goes on to say that the Canadian force "has re-taken control of the two remaining detainees and intends to have them interviewed at KAF as soon as possible."

It is unclear why the Canadians took back the two men. It could have been their plan all along, or they could have acted out of frustration at the loss of the third man, The Globe reported. 

Another possibility is that the Afghan army did not have the ability to return the prisoners to KAF.

The battle occurred just one month after reports emerged that Canadian soldiers had twice intervened to stop the summary execution of Taliban suspects held by the Afghan army.

The prisoner handover agreement was criticized earlier this month when news broke that three Afghan prisoners, considered key witnesses in a probe into allegations of abuse by Canadian soldiers, had disappeared.

Since then, Canada has announced a deal with the Afghanistan Independent Human Rights Commission to have them monitor and report on detainee abuse.

Defence Minister Gordon O'Connor has also taken heat for claiming that the International Committee of the Red Cross (ICRC) monitored the treatment of the detainees and would report back to Canadian officials if anything was wrong.

The ICRC denied the claims, saying they would never tell Ottawa about any abuses as they can only make known assessments or interventions to the government whose facilities they are visiting.