In the crash of a gyrocopter, the two inmates were killed on Saturday west of the small town of Butzbach in Hesse.
The victims are two men aged 39 and 47 from Baden-Württemberg.
Why the ultralight aircraft crashed in the afternoon in the Wetterau district between the city of Butzbach and Butzbach Airport in a forest area was initially unknown.
Experts from the Federal Bureau of Aircraft Accident Investigation should clarify this question, the police said.