NEW YORK, Sept 2: American investigators, who have spent months trying to unravel the plot that resulted in the attacks on New York City and Washington, are worried about key figures in the Sept 11 conspiracy who got way, and are planning more attacks against the United States.

CIA officials told Newsweek magazine that they include Khaled Shaikh Mohammed and others who are on a mission to destroy America, and at least three other men whom investigators have identified as the planners and financiers of the attacks.

“They are believed to be in hiding, where they may be planning future strikes,” the magazine says.

“Sept 11 demonstrated to us that you don’t need a large number of people or a huge infrastructure to do a lot of damage. There are still a lot of people out there who can do some real harm.”

The magazine said that the investigators have reason to believe that Mohammed is not only alive, but hard at work. US officials said they have evidence linking Mohammed to the April bombing of a synagogue in Tunisia, which killed 21 people. The suicide bomber phoned Mohammed just three hours before blowing himself up.

A senior official told Newsweek that US intelligence believes Mohammed had a powerful collaborator in planning the strike: Saad bin Laden, a son of Osama bin Laden.

Agents didn’t realize just how important Mohammed was in planning the Sept 11 attacks until April this year, when they captured Abu Zubaydah.

Inside Zubaydah’s safe house, they discovered a large cache of information about the plot, and sources said Zubaydah himself confirmed to investigators that Mohammed was one of the key Sept 11 conspirators.