An "Islamist" suspect has been detained by police investigating a bomb attack on the Borussia Dortmund team bus.
"Two suspects from the Islamist spectrum have become the focus of our investigation. Both of their apartments were searched, and one of the two has been detained," said Frauke Koehle, from the federal prosecutor's office.
She said the explosives used in Tuesday's attack contained metal pins - one of which buried itself into a headrest on the coach - adding it was lucky "nothing worse happened".
German Chancellor Angela Merkel described it as a "repugnant act", saying she was "horrified".
Three identical letters left at the scene of the three blasts linked the attack to German involvement in the fight against Islamic State in Syria.
They mentioned the Berlin Christmas market attack carried out by an IS-inspired terrorist in 2016, according to the Sueddeutsche Zeitung newspaper.
The letters, reportedly written in German, began: "In the Name of Allah, Most Gracious, Most Merciful."
They also said sports stars and other prominent people "in Germany and other crusader nations" were on a "death list of the Islamic State".
The threat would last until German planes are withdrawn from the war zone, and the US airbase at Ramstein, near the French border, is closed, the letters added.
They were found near the team coach and their authenticity is being verified.
Detectives have not ruled out the possibility that it might be a deliberate attempt by the attackers to mislead investigators.
A fourth letter posted online claiming responsibility, which could have come from anti-fascists, has been discounted by police following "serious doubts" over its authenticity.
Spain international Marc Bartra underwent surgery for a broken bone in his hand after being injured by shattered glass from the coach's windows.
He posted a photo on Instagram and tweeted on Wednesday afternoon: "Hello! As you can see I am doing much better.
"Thanks for all your messages! All my strength to my team mates, fans and to Borussia Dortmund for tonight!"
Other Dortmund players, including former Chelsea midfielder Andre Schuerrle, returned to training a day after the blasts, with the club's chief executive, Hans-Joachim Watze, tweeting to say the team will "not give in to terror".
The team's Champions League quarter-final first leg against Monaco, which was postponed on Tuesday, kicked off at 5.45pm on Wednesday, with Dortmund supporters chanting "Bartra! Bartra!" just before the match got under way.
Monaco won the match 3-2.
Officers are still investigating three "serious explosive devices" which went off as the players and coaching staff left the L'Arrivee Hotel and Spa on the outskirts of Dortmund shortly before Tuesday's match had been due to take place.
They believe the explosives may have been hidden in a hedge near the car park.
Ralf Jaeger, the interior minister for North Rhine-Westphalia state, said security had been stepped up in Dortmund, including at the club's training ground and stadium.
"We might assume that further attacks are planned and we need to take these things seriously," he said.
Monaco fans were offered a place to stay for the night by Dortmund supporters on social media after the match was postponed for 24 hours.
The German club sent out a tweet about the scheme under the hashtag #bedforawayfans.
Fans of both clubs posted pictures of themselves enjoying meals and a drink together.
Monaco also offered its fans €80 (£67) each to stay in a hotel for the night.