German police have detained a suspect with "Islamist links" following a bomb attack on the bus of the Borussia Dortmund football team, the BBC reported on Wednesday.
Prosecutors also said the three explosive devices contained metal pieces.
Two letters claiming the attack on Tuesday evening were being investigated, they said.
Prosecutors are treating the blasts as a terrorist attack but say the precise motive is unclear at present.
Chancellor Angela Merkel on Wednesday said the attack was "an appalling crime" and praised the fans of both Dortmund and their Champions League opponents, Monaco, for coming together.
Fans later filled Signal Iduna Park in Dortmund for the rescheduled quarter-final first-leg, which kicked off at 18:45 local time (16:45 GMT).
There was a rousing rendition of You'll Never Walk Alone by both sets of fans before kick-off.