The 21-year-old man remained in custody by an investigating judge in Karlsruhe on charges of attempted murder, belonging to a terrorist organization and attempting to cause an explosion.

The man, who was identified as Youssef Mohamad, was arrested on Saturday in a police raid on the railway station in Kiel as he tried to flee the northern city, where he was a student.

He was transported to Karlsruhe by helicopter on Sunday, handcuffed and in overalls and questioned by authorities.

The man's fingerprints and DNA were found on one of the two suitcases in which homemade bombs were planted on trains traveling through Dortmund and Koblenz on July 31, according to Federal Prosecutor General Monika Harms.

Little is known about the second suspect, except that he is not German, about 20 years old and does not live in Kiel, according Jörg Ziercke, head of the Federal Crime Office.

"We do not know how the second suspect is going to react," he added.

Suspects may be part of German terrorist organization

The police have not ruled out that the planned attacks could have been motivated by the situation in the Middle East, according to Ziercke.

"My impression is that there were more people involved in the background," August Hanning, state secretary for the interior, told German public broadcaster ARD on Monday.

The bombs, which failed to explode due to a construction error, consisted of gas canisters, alarm clocks, wires and batteries and had been timed to detonate at 2:30 p.m., 10 minutes before the trains arrived at the stations, and would have turned the trains into "balls of fire," according to prosecutors in Karlsruhe.

"We are now working on the basis that this was the work of a terrorist group based in Germany and that it was an attempt to kill a large number of people," Rainer Griesbaum, a federal prosecutor, told reporters.

The judge heard that the two suspects met at the station in the southwestern city of Cologne three weeks ago, where they boarded trains bound respectively for Dortmund and Koblenz.

Media pressure led to arrest

German media on Sunday continued to run photographs of the suspects, both young men with dark hair, captured on closed circuit television cameras at Cologne station.

The pictures led to the arrest of the first suspect, and police hope it can also help them to snare the second, Ziercke said.

The prosecutor's office on Sunday said police have searched the student dormitory in Kiel where the arrested suspect lived and a neighboring property but found no explosives.

A note in the case found in Koblenz contained Arabic writing, a Lebanese telephone number and packets of starch with labels in Arabic.

Bild am Sonntag newspaper said fellow students had told the investigators that the arrested suspect had recently visited Lebanon after his brother was killed in an air raid in the Israeli offensive on the country.

A student in Kiel, Sebastian Walter, told N24 television news channel that the man was "very polite and friendly." Another mentioned that he "very often spoke about religion."

Calls for tighter public security

Interior Minister Wolfgang Schäuble late Saturday warned that the security situation in Germany was "exceptionally serious."

"The threat has never been so close," he told ZDF television. "We do not know what could still happen."

Wolfgang Bosbach, deputy head of the conservative Christian Democratic party in parliament, said he hoped the failed attack would be a wake-up call for those opposed to tighter security.

Schäuble said the time had come to adopt legislation on a so-called "anti-terror database," which has been in the pipeline for some time but has been mired in controversy.

But Social Democratic Party leader Kurt Beck and members of the opposition Green and Left parties warned against an over-reaction that would infringe on people's right to privacy.