A signal controller who was in charge when two German trains crashed killing 11 people has admitted to playing a game on his mobile phone that day.
The man was detained following developments in the investigation into the head-on train crash in Bavaria in February.
The public prosecutor's office said investigators had found the man "turned on his mobile phone during his shift on the morning of the accident, started an online computer game and played actively...until just before the collision of the trains."
He faces possible charges of causing death through negligence.
It was Germany's biggest train crash since 1998.
The man denied being distracted by the computer game, but the prosecutor's office said the time period in which he was found to be playing the game meant it could be expected that he was not paying attention to a critical traffic intersection.
The controller gave the trains an incorrect signal and then hit the wrong buttons when issuing a distress signal, meaning it was not heard by the train conductors, the prosecutor's office said.
The trains, carrying about 150 people in all, crashed at high speed between the spa town of Bad Aibling and Kolbermoor, near the Austrian border.
The investigation is continuing.
No evidence of technical problems has been found to date.