OTTAWA - Canada's top military cop was cleared Tuesday of potential criminal wrongdoing in the ongoing legal controversy involving Afghan detainees.

The Canadian army says there's no evidence to support a prosecution of naval Capt. Steve Moore, the provost marshal.

The conclusion was reached following an investigation by two senior RCMP officers, who'd been called in by the military after allegations of abuse of Taliban prisoners surfaced last winter.

A spokeswoman for the National Investigative Service -- a branch of the Canadian Forces -- characterized the investigation, which to this point had remained a secret, as procedural.

"The provost marshal himself is in the direct chain of command and the allegations had a potential criminal angle,'' said Capt. Cindi Tessier.

The decision to conclude the investigation comes as human rights lawyers are set to appear in court Wednesday for another round in the legal battle over detainees.

Concern that prisoners captured by Canadians and handed over to Afghan authorities faced possible abuse and even torture, has spawned a dizzying array of investigations and court actions.

Tessier said that a separate national investigative probe is still underway into whether individual military police officers in Afghanistan could be held accountable if abuse has taken place.

Amnesty International Canada and the British Columbia Civil Liberties Association complained last February to the Military Police Complaints Commission, accusing military cops of exhibiting "a wilful blindness to the consequences of transferring detainees and that they may have aided or abetted the torture of detainees.''

The agency is still investigating that accusation, said Stan Blythe, chief of staff to the commissioner.

"We were aware the (military) police were looking at the possible criminal side of this and have received a copy of their investigation,'' he said.

"We're aware of it and will make use of the information they've discovered, but it doesn't close the investigation for us.''

To date, Canadian authorities in Kandahar have received six complaints from Afghans who say they were abused after being handed over to local authorities.

Amir Attaran, the University of Ottawa law professor who's been pushing the issue of detainee rights, was mystified at how RCMP investigators could clear the provost marshal when Defence Minister Peter MacKay acknowledged the alleged cases of abuse last spring, when he was foreign affairs minister.

"Peter MacKay has said Canadian investigators have heard, quote, serious allegations of torture; he called them serious, that was his word,'' said Attaran.

"How can he call them serious when his own staff now says there's no evidence?''

Both Amnesty and the civil liberties association have launched a court challenge, trying to stop the transfer of prisoners to Afghan jails, but that action has been bogged down in a quagmire of legal wrangling.

The case had been set to go before a Federal Court judge last spring, when the Conservative government announced it had reached a new understanding with the Afghans, giving Canadian authorities better access to detainees. The challenge was put on hold until the human rights groups could review the deal.

A further snag developed in early July when officials at National Defence denied an application for documents filed by Amnesty lawyers.

The records were deemed too sensitive to be released and when human rights lawyers challenged it, the government invoked an unusual section of the Canada Evidence Act, which dropped a cloak of secrecy around the entire challenge.

Paul Champ, a lawyer for Amnesty, said in addition to fighting for the Afghan documents, his group has launched a charter challenge, hoping to quash the government's power to force secret hearings on court applications.

"The government secrecy privilege is an exceptional power that should only be used sparingly in a democracy,'' he said.

"Holding hearings in secret doesn't allow for oversight by the justice system, the media and the public.''

The Canadian Association of Journalists has signalled its intention to intervene in the charter case, supporting Amnesty's application as it relates to the Evidence Act.