A person from the "Islamist spectrum" was detained Wednesday in connection with the Borussia Dortmund soccer team bus attack in Germany that injured a player, German prosecutors said.

Authorities are focused on another suspected extremist who may also be involved in detonating three explosives on Tuesday, Frauke Koehler, a spokeswoman for the prosecutors, said. A letter turned up near the site claiming responsibility and suggesting a possible Islamic extremist motive for the attack.

Crews searched the apartments of both suspects.

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Koehler said three copies of the note were found and they called for the withdrawal of German Tornado reconnaissance jets from Turkey and the closure of the United States' Ramstein Air Base in Germany.

Investigators are still evaluating its credibility, though they suggest that "an Islamic extremist background to the attack appears possible," Koehler said.

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The letter could be genuine or "an attempt to lay a false trail," leading authorities to investigate every possible motive in the case, Ralf Jaeger, the interior minister of North Rhine-Westphalia state, said. German news agency dpa initially reported that police were looking at multiple leads.

"It could be left-wing extremism or right-wing extremism. It could be the violent fan scene, it could be Islamic extremism," Jaeger added.

Borussia Dortmund was heading to their Champions League quarterfinal match against Monaco when the attack happened. The explosive devices contained metal pins, one of which buried its way into a headrest on the vehicle, Koehler said.

The match was rescheduled for Wednesday.

Dortmund defender Marc Bartra was injured and needed surgery for injuries to his wrist and arm.

German Chancellor Angela Merkel contacted the team, wishing them "all the best," spokesman Steffen Seibert told reported Wednesday. She was "dismayed" and condemned the attack.

The Associated Press contributed to this report.