The massive search to uncover the terrorist plot stretched from Miami to Boston to Portland, Maine and on to Canada and Germany, say reports. Up to 50 people are believed to have taken part in the attack, the Justice Department said, with at least four hijackers trained at U.S. flight schools. Internet service providers said they were complying readily with FBI search warrants seeking information about an e-mail address believed connected to the attacks. By Wednesday, authorities had detained at least a half dozen people in Massachusetts and Florida on unrelated local warrants and immigration charges and were questioning them about their possible ties to the hijackers who commandeered four commercial American aircraft. A Venice, Fla., man said FBI agents told him that two men who stayed in his home while training at a local flight school were involved in the attacks. Charlie Voss, a former employee at Huffman Aviation in Venice said the FBI told him one of men was named Mohamed Atta. A student at Huffman Aviation identified the second man as Marwan Alshehhi. Citing federal authorities, The Miami Herald reported Thursday that Atta was one of four suspects who died on American Airlines Flight 11, the first jetliner to crash into the World Trade Center. Thursday morning, police detained one man in the northern German city of Hamburg in connection with the attacks, authorities said. The man was held for questioning as part of an investigation, said Gerhard Mueller, the state police chief. He refused to give the man’s name, age or nationality.