The Lebanese man accused of masterminding a plot to destroy Hudson River train tunnels to bring death and flooding to lower Manhattan had visited the United States at least once - a trip to California six years ago, a federal law enforcement official said. The official, speaking on condition of anonymity because the investigation is ongoing, said 31-year-old Assem Hammoud was in the U.S. on a legitimate visa for a brief stay, and that he was believed to have been visiting either family or friends. The visit occurred long before authorities say the tunnel plot began to unfold. Authorities are still trying to trace Hammoud's steps during that trip but say they have no record of him going to New York. They have not ruled out the possibility that Hammoud had come to the country using different names.Meanwhile, a senior Lebanese official said authorities there found maps and bombing plans on the personal computer of the suspect. Acting Interior Minister Ahmed Fatfat described the information found on Hammoud's computer as "very important." "It contained maps and bombing plans that were being prepared," Fatfat said in a local television interview. Lebanese security officials told The Associated Press that they obtained "important information" from Hammoud's computer and CDs seized from his office at the Lebanese International University, where he taught economics. "This information helped the investigators make Hammoud confess to his role in plotting a terror act in America," one Lebanese official said, speaking on condition of anonymity because of the sensitivity of the case.