CSIS watched terrorist suspect in 1999

Canadian spy agency had terrorism suspect under watch two years ago

A Mauritanian man arrested in West Africa on the weekend for alleged involvement in the Sept. 11 terrorist attacks was under surveillance by the Canadian Security Intelligence Service two years ago.

Mouhamedou Ould Slahi is thought to have ties to Osama bin Laden, the man the United States says is behind the suicide hijackings.

Investigators believe Slahi, 31, might be directly involved in the plot that destroyed the World Trade Center in New York and heavily damaged the Pentagon.

He is also connected to Ahmed Ressam, who was convicted earlier this year of plotting to blow up Los Angeles International Airport.

Ressam, a former Montreal resident, was arrested at a Washington state border crossing with a trunk loaded with explosives in December 1999.

Slahi was arrested in January 2000 in Dakar, Senegal, and sent to Mauritania where FBI agents interrogated him. He was later released.

After living in Germany for several years and studying engineering at the Gerhard Mercator University, Slahi made several trips to Montreal in 1999.

Three of the terrorists U.S. officials say crashed the four jets on Sept. 11 studied at the same university, including Mohammed Atta, thought to be one of the ringleaders.

U.S. and Canadian investigators think Slahi was sent in 1999 to activate a terrorist cell based at a Montreal mosque. They suspect he directed the millennium bombing plot involving Ressam.

An official with CSIS confirmed Slahi was under surveillance for several weeks while he lived at the Montreal mosque, but was allowed to leave Canada because there were no grounds to hold him.

Slahi denies he directed Ahmed Ressam. In a recent trial Ressam said he was instructed on how to set bomb timers and where to leave his explosives at the L.A. airport, but U.S. authorities insisted he conceal the identity of his adviser.

Slahi is related by marriage to bin Laden associate Abu Hafs, also known as Mahfouz Ould al-Walid, who appears on a list of 27 people and groups whose assets have been seized by the U.S. government because of links to terrorism.