German prosecutors formally arrested on Sunday (August 20) one of the men who is suspected of planting makeshift bombs on German trains last month with the intention of killing a high number of people. An investigating judge at the Federal Prosecutors Office in Karlsruhe questioned the man and issued a formal warrant for his arrest. The federal prosecutor said the man was suspected of belonging to a terrorist group and of trying to commit murder on a large scale. According to authorities the plot to blow up passenger trains had only failed because the bombs didn't go off. The federal prosecutor has described the man who police seized in the northern city of Kiel as a 21-year-old Lebanese student named Youssef Mohamad E.H., who was living in Germany for two years. Germany has not suffered the kind of attacks that have killed scores on public transport in Britain and Spain in recent years. But on Friday it emerged that two men, who may have been part of a wider Islamic militant network, had come close to exploding makeshift bombs on two trains in Dortmund and Koblenz last month. On Saturday, German police detained the man suspected of planting the bombs as he was trying to leave Kiel station. The two were caught on video cameras in Cologne train station, dragging suitcases which contained the explosive devices onto the trains. Although the bombs -- made with propane tanks and crude detonating devices -- failed to go off, authorities say the complexity of the plot suggests the men had not acted alone. The second suspect is still at large and the focus of an intense manhunt. News of the failed bomb attack came a week after Britain said it had foiled a plot to blow up transatlantic airliners, and amid intense debate in Germany over government plans to send troops to Lebanon as part of a U.N. peacekeeping force.