German police have detained a suspect with "Islamist links" following a bomb attack on the bus of the Borussia Dortmund football team.
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). Dortmund lost 3-2.
Afterwards, Borussia Dortmund manager Thomas Tuchel said his club felt "completely ignored" over the rescheduling of the match.
"We would have liked more time to take stock," he said.
Fans unite at match : Gavin Lee, BBC Europe reporter, Dortmund
Inside a hotel close to the Dortmund stadium, several of the Monaco team told me how they discussed going ahead with the match.
Some were worried about the implications of the attack, and the risk of more danger, but felt reassured by German security, and ultimately felt to postpone was to give in, and that they were not prepared to do. The players' bus waiting outside was under constant surveillance by armed police.
As the match finally got under way this evening, under intense security, all fans sang "You'll Never Walk Alone" together. Players warming up applauded the support.
One fan said his wife would not let him bring his children because "the mass congregation of people outside made the venue too big a target".
Others were defiant. German and French fans said they had become used to living with the threat of terrorism, and would not be stopped from enjoying their lives: the game would go on.
Dortmund player Nuri Sahin gave an emotional interview after the match, saying: "Last night I didn't realise what happened and, when I was at home, my wife and my son were waiting for me in front of the door and then I felt how lucky we were.
"We love football, we suffer with football. I know we earn a lot of money and have a privileged life, but we are human beings. There is so much more than football in this world and last night we felt it."
Earlier, a spokeswoman for Germany's federal prosecutor, Frauke Koehler, said: "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."
German media are reporting that the suspect detained is a 25-year-old Iraqi, and the second suspect is a 28-year-old German.
The blast radius of the attack was about 100m. Prosecutors said it was lucky the casualties were not worse.
Ms Koehler said a piece of shrapnel had embedded itself in the headrest of one of the seats on the team bus.
She said three copies of the same letter were found near the site of the blasts, indicating that the attacker had links to so-called Islamic State (IS). IS had said it carried out the attack on a Christmas market in Berlin in December that killed 12 people.
Ms Koehler said the letter demanded "the withdrawal of [German] tornado fighter jets from Syria and, I quote, the closure of Ramstein airbase".
Ramstein is a significant US Air Force base. The text is being analysed to see if it is authentic.
The Sueddeutsche Zeitung newspaper said the letter began with the phrase "in the name of Allah". But it said it was possible the perpetrators were deliberately trying to mislead the investigation.
A second letter was published online, in which left-wing extremist groups claimed to have carried out the attack, but prosecutors had reason to believe this letter was not authentic.
What happened on Tuesday evening?
Borussia Dortmund players were on their way to the match, when three explosive charges detonated, police said.
Spain international Marc Bartra underwent an operation after breaking a bone in his wrist. No other players were hurt, but a police officer on a motorbike escorting the bus suffered trauma from the noise of the explosions.
The blasts brought the best out of the fans.
Dortmund residents offered Monaco fans a bed for the night on #bedforawayfans.