Lawyers for one of only three men in Canada subject to a restrictive federal security certificate grilled a spymaster on Wednesday about how CSIS kept tabs on their client.

Mohamed Mahjoub, a refugee from Egypt, has been imprisoned or under house arrest since 2000 based on secret information and without ever facing any charges, because the federal government deems him a threat to national security.

The latest round of his battle to have his security certificate revoked unfolded Wednesday in an Ottawa court, where Mahjoub's lawyer Paul Slansky questioned the Canadian Security Intelligence Service's head of operations for the Toronto area.

CSIS supervisor Paul Vrbanac was pressed on whether the intelligence agency intercepted Mahjoub's communications for longer than a court had authorized. Vrbanac was also asked how CSIS kept tabs on Mahjoub, and how the agency determined that he had links to particular organizations.

Mahjoub took part in the session via video conference from Toronto, where he's under house arrest.

His hearings are scheduled to continue until November, following which Federal Court Judge Edmond Blanchard could revoke the security certificate against him or find it reasonable — in which case the federal government would likely move to have Mahjoub deported.

Indefinite detention

Security certificates allow the government to detain permanent residents and foreign nationals that it deems to be a threat to national security, without charging them and based on information they and their lawyers aren't allowed to see. If the certificate is upheld in court, they can be deported, but when they face a threat of torture or death back home, they could be kept indefinitely in a Canadian immigration prison or under house arrest.

In the case of Mahjoub, 51, an Egyptian citizen and father of three living in Toronto, the government alleges he had high-level links to a militant organization in Egypt, which he fled in the mid-1990s.

Part of Ottawa's case against Mahjoub consisted of summaries of wiretapped conversations between 1996 to 2001; the original, full records had been destroyed. In June, Judge Blanchard ruled that the destruction of the originals violated Mahjoub's right under the Charter of Rights and Freedoms to disclosure of the information being used against him. He also said there was no way to measure the accuracy of the summaries.

That was the second blow to the government's case in a month. Earlier, Blanchard dismissed 11 federal lawyers and assistants from the case because the government took confidential files belonging to Mahjoub's legal team from a locked courtroom.

Last December, a Canadian Press report revealed CSIS has known for years that the "bulk of the information utilized in Mr. Mahjoub's certificate" came from foreign government agencies that use torture.

6 certificates since 2000

In the last 12 years, security certificates have been used to arrest five Arab men, all of them on accusations of ties to al-Qaeda or related organizations. Two of the men — Hassan Almrei and Adil Charkaoui — have since had their certificates rescinded by courts. The remaining three, including Mahjoub, are under house arrest in Ontario. A security certificate has also been issued against one Russian man thought to be a spy who agreed to be deported.

The Supreme Court of Canada ruled in 2007 that the entire security certificate process was unconstitutional, but it allowed Parliament to make modifications, particularly to how secret information can be contested by "special advocate" lawyers approved by the government.