“If we hadn’t here and there gotten little puzzle pieces of information, often through coincidences, we wouldn’t have found them,” said the intelligence official. He said the men were not only trained in explosives, but also in countersurveillance.  It was a mistake by a police officer the day before the arrest, the official said, that may have accelerated both the suspected plot and the arrest. The officer pulled the three suspects over for driving with their high beams on. During the traffic stop, he said that the men were on the watch list of the German Federal Police. The suspects heard him, the official said, and so did the federal officers, listening on the wiretap.  A German police official involved in the investigations of Islamic terrorism in southern Germany for several years said that “since 9/11, any information that had to do with the Islamic scene has been sent to the Americans,” including information about members of the suspected plot.  The discussion was going on at the top levels of government as well. President Bush and Chancellor Angela Merkel were reported to have discussed the investigation at the Group of 8 conference in June, the German news magazine Spiegel said on its Web site on Saturday.  Investigators here said Saturday that they fear that terrorist plots could still be under way in Germany by unarrested members of the Islamic Jihad Union cell.  A senior investigator on the case, speaking on condition of anonymity, said there might be “parallel planning” for separate attacks by members of the group. “There are still three of them out there who have trained with explosives in the camps and these people are still free,” the investigator said.  The fear of parallel plots was also spelled out in the confidential investigative report, which said, “At the moment it cannot be ruled out that unexposed members or sympathizers of the I.J.U. are adhering to the original plans.”  Katrin Bennhold contributed reporting from Neuenkirchen, Germany.  A version of this article appears in print on , on Page 120 of the New York edition with the headline: Germans Say U.S. Officials Helped to Foil Bombing Plot. Order Reprints| Today's Paper|Subscribe
American intelligence intercepted e-mail messages and telephone calls between Germany and both Pakistan and Turkey that raised red flags last year.