One person has been detained in connection with the attack on the Borussia Dortmund football team bus, and German prosecutors say a letter found near the scene suggests a possible Islamic extremist motive for the blasts.

Spokeswoman Frauke Koehler said on Wednesday that two suspects from the “Islamist spectrum” had become the focus of the Dortmund investigation.

She said at a news conference their apartments were searched and one of them had been detained.