The public inquiry investigating what happened to Syrian-born Canadian Maher Arar has begun. But much of the crucial evidence could be kept under wraps because of security concerns.

In the end, Justice Dennis O'Connor will decide what stays private, and what is made public. 

Barbara McIsaac, lawyer for the attorney general, says "several thousands of pages" of documents from various federal agencies have been turned over to the commission. Still, certain sensitive records are likely to be shielded from public view, and some testimony is expected to be heard behind closed doors.

Arar, 34, was deported to Syria by the U.S. as a suspected terrorist in September 2002 and  jailed without charge.

Arar says he was beaten, tortured and forced into giving false confessions while locked in a tiny cell for more than 10 months. He was eventually released without explanation and returned to Canada.

"I think the Canadian public wants to know how it is possible that a Canadian citizen gets shipped off to torture based on the information provided by the Canadian security services," Maher's lawyer Lorne Waldman told reporters Monday.

The Canadian Security Intelligence Service and the RCMP have already said they did nothing wrong.

The inquiry's first couple of weeks will provide the general context of how the relevant government agencies operate. It likely won't be until next month that the hearings delve into the substance of how officials handled Arar's case.

"What we're hoping here is to understand how this complex relationship exists after 9/11," Arar says.

The inquiry's first witness was former CSIS head Ward Elcock, saying there are a lot of checks and balances overseeing the spy agency.

Elcock says CSIS is monitored by two watchdogs, an auditor general and a human rights commission. It is also watched by the federal access-to-information regime.

"I think it has made it a much stronger organization," he told the inquiry.

O'Connor's inquiry will try to answer questions about what role Canadian security officials played in the affair.

Arar has consistently denied being a terrorist and says Canadian intelligence authorities played a role in his ordeal. He accuses them of shoddy intelligence work, racial profiling and says they were aware he was going to be deported.

"I've heard myself, a lot of stories where CSIS and RCMP have used questionable methods and I hope the commissioner will look at the systemic issue," Arar said.

The inquiry is expected to run well into the fall.

Arar and his family have also launched a multi-million dollar lawsuit against the Canadian government, CSIS, and the RCMP, alleging they worked together to investigate him on the basis of stereotypes and prejudices.