Federal prosecutors accused Kerim Marc B., a German citizen, of participating in weapons training with ISIL and fighting with the militants in Syria. The man travelled to Syria through Turkey in March 2013 and had joined up with the Islamic State by October. Early in 2014 he came back to Germany, but in July returned once again to the warzone in Syria.
According to media reports, the suspect was seeking treatment in Germany to extract grenade shrapnel from his body, but changed his mind and returned to the Middle East.
Dusseldorf prosecutors said they were initially investigating Karim Marc B. on the suspicion of planning attacks in Germany, when it became known that he had actually joined ISIL.
The suspect will face charges on Thursday and the custody terms will be set. The investigation continues.
Approximately 600 German citizens have left the country to fight in Syria with about 70 being killed there, according to German officials.