Latest: Suspect arrested by police investigating Dortmund attack

Latest: German prosecutors say a letter found near the scene of the Dortmund team bus blasts suggests a possible Islamic extremist motive for the attack, and one suspect has been taken into custody.

Update 2.30pm: German prosecutors say a letter found near the scene of the Dortmund team bus blasts suggests a possible Islamic extremist motive for the attack, and one suspect has been taken into custody.

Frauke Koehler, a spokeswoman for federal prosecutors, said that two suspects from the "Islamist spectrum" have become the focus of the Dortmund investigation.