German authorities arrested a suspected Islamic extremist on Wednesday, a day after explosions hit the Borussia Dortmund football team’s bus.
Police believe the three explosives used contained metal pieces and they are investing two letters that were found near the scene.
Investigators are treating the incident as a terrorist attack, but say they are still looking into the precise cause and motive.
Chancellor Angela Merkel condemned the attack, calling it an appalling crime and praised the fans of both Dortmund and their Champions League opponents, AS Monaco, for coming together.
Dortmund defender Marc Bartra, who broke his wrist in the incident, took to Instagram to thank fans for their support.
The postponed quarterfinal first leg, held on Wednesday evening local time, ended in a 3-2 defeat for Dortmund.