Berlin ? A Turkish man and his American fiancee appear not to have had the backing of terrorist networks in an alleged plot to bomb the U.S. Army base at Heidelberg on the anniversary of Sept. 11, the German Interior Ministry said Saturday.

The couple, who were arrested Thursday when police confiscated bomb-making materials and Islamic literature from their apartment outside Heidelberg, about 480 miles southeast of Berlin, were portrayed by authorities as being sympathetic to Osama bin Laden but lacking connections to extremist cells and militant groups.

“Based on what we know so far, we are dealing with an individual (the Turkish man) who has shown no indication of participation in a terrorist network,” German Interior Minister Otto Schily told Antenna Bayern Radio on Saturday. “It seems we are dealing with a dangerous individual with an Islamic background.”

The couple identified Saturday as Oman Petmezci, 24, of Turkish origin, and his American-born fiancee, Astrid Eyzaguirre, 23 espoused deep hatred for Americans and Jews, according to friends and law enforcement officials. Their alleged plot to explode bombs at the U.S. Army base where Eyzaguirre worked in a post exchange would have struck at the core of the American military presence in Europe.

The Heidelberg base is the U.S. Army’s European headquarters and home to 16,000 soldiers, civilians and dependents. Police allege that Petmezci, employed by a chemical warehouse in Karlsruhe, had amassed 287 pounds of chemicals and explosive materials, including five pipe bombs, for a Sept. 11 attack.

According to a report Saturday in the German magazine Der Spiegel, a friend of Eyzaguirre told U.S. military police that Eyzaguirre had told her she sympathized with bin Laden and had warned her to stay away from the Army base in the days leading up to Sept. 11. U.S. authorities then tipped off German law enforcement agencies, which on Thursday raided the couple’s third-floor apartment in Walldorf.

Despite Schily’s playing down the possibility that the alleged plot was part of a broader conspiracy involving al-Qaida remnants or sleeper cells, some German officials expressed concerns that a mastermind lurks behind Petmezci and Eyzaguirre. The German government has been criticized for not closely tracking terrorists groups in Hamburg, where Mohamed Atta and other hijackers plotted strategies for the Sept. 11 attacks on New York and Washington.

“It’s not very likely that a warehouse worker,” Bavarian Interior Minister Guenther Beckstein said of Petmezci, “could by himself build explosives out of chemicals and make an ignition switch out of electronic parts. … He must have had instruction.”

German TV reported that Petmezci might have had links to Islamic groups, including a center in Heidelberg that was under suspicion for financing the 1998 bombings of two U.S. embassies in Africa.