A suspect has been detained by police probing the Borussia Dortmund team bus blasts after two people with Islamist backgrounds became the focus of a police investigation.
The German prosecutor's office said both their apartments were searched, which led to one being held, after a still-unverified confession letter found at the scene of Tuesday's triple blast suggested an Islamic extremist motive.
Spokesperson Frauke Koehler also confirmed:
The letter found at the attack site demanded the withdrawal of German Tornado reconnaissance jets from Turkey and the closure of the United States' Ramstein Air Base in Germany.
Authorities are still evaluating the letter's credibility.
Authorities had 'significant doubts' that a separate apparent online claim of responsibility from anti-fascist extremists was valid.
Three explosive devices used in the attack were equipped with metal pins, one of which buried its way into a headrest on the bus.
The type of explosives and the method for setting them off was still being investigated.
The team could consider themselves lucky 'that nothing worse happened'
According to earlier media reports, the letter found at the blast site made reference to December's attack on the Berlin Christmas market and German military operations against so-called Islamic State.
German newspaper Sueddeutsche reported the unsigned letter began with the words: "In the Name of Allah, Most Gracious, Most Merciful."
Federal government officials had brought in Islam experts to examine if the letter is genuine or potentially a hoax attempt to wrong-foot investigators.
German Chancellor Angela Merkel meanwhile condemned the attack on the Bundesliga team bus as "repugnant".
Mrs Merkel's spokesperson said she had spoken with Dortmund's chief executive to express her digust at the blasts.
"The chancellor was last night, like people in Dortmund, like millions everywhere, appalled by the attack on the BVB team bus," Steffen Seibert said.
"One can only be relieved that the consequences were not worse."
The blasts shattered windows on the bus as the team left their hotel for their Champions League match with Monaco around 7.15pm on Tuesday.
The quarter-final first leg was rescheduled to Wednesday evening with heavy security ramped up in the German city.
Dortmund's Spanish defender Marc Bartra had an operation after injuring his wrist and arm.
Police also said an officer who was accompanying the bus on a motorbike suffered blast trauma and shock.
Monaco fans were offered overnight accommodation after Dortmund began using the hashtag #bedforawayfans to help supporters stranded in the city.