German police have detained one suspect with apparent "links to so-called Islamic State" in the wake of the attack that hit Borussia Dortmund's team bus ahead of Tuesday's Champions League encounter with Monaco.
The vehicle was damaged as three explosions occurred while the coach was making its way from the team hotel to Signal Iduna Park for the quarter-final first-leg tie.
Marc Bartra was injured in the incident, with the club confirming on Wednesday that the defender had successfully undergone surgery on his right wrist.
Police found three letters claiming responsibility for what they described as a "targeted attack" on the Dortmund bus and one person has now been arrested following searches at the apartments of two suspects.
"Three letters containing the same text have been found near the site of the blasts. Links to so-called Islamic State appear to be a realistic option based on these letters," Frauke Koehler - a spokeswoman for Germany's federal state prosecutor in Karlsruhe - stated at a news conference.
"Among other things they demand the withdrawal of German tornado fighter jets from Syria and the closure of Ramstein airbase.
"The letter is being analysed by experts for its authenticity. There is therefore no final conclusion as of yet.
"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."
Another letter was published online in which left-wing extremists claimed responsibility for the attack, but the federal prosecutor has doubts over the authenticity of said letter.
Tuesday's encounter was postponed until Wednesday, with UEFA undertaking a review of security procedures for all matches, as Atletico Madrid host Leicester City, and Real Madrid head to Bayern Munich.