Story highlights Three explosives went off, one failed, authorities say

Defender Marc Bartra in surgery to repair broken bone in arm, team says

(CNN) Three explosives that shattered windows and injured a player on the Borussia Dortmund team bus Tuesday as the German football squad was en route to its home Champions League match were part of a targeted attack, police said.

Investigators found near the scene a handwritten letter that claimed responsibility for the attack, prosecutor Sandra Luecke said.

One explosive device failed to go off, Luecke said.

Dortmund police Chief Gregor Lange said police have not ruled out any possible motives for the attack, which led to the match being postponed until Wednesday night.

Marc Bartra of Borussia Dortmund was injured in the blasts, the team says.

Spanish defender Marc Bartra, 26, suffered injuries to an arm and hand, the team said. Bartra, who has played 29 games in all competitions for Dortmund this season, was treated at the scene and hospitalized.

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