BERLIN (AP) — Prosecutors say they have charged a German man with murder and committing a war crime for allegedly helping torture and kill prisoners as a member of the Islamic State group in Syria.

German federal prosecutors said Thursday that the new charges against 27-year-old Nils D., whose surname wasn't provided in line with privacy rules, were filed at the Duesseldorf state court earlier this month.

Nils D. traveled to Syria in October in 2013, returned to Germany about a year later and was arrested in January 2015.

The suspect was sentenced in 2016 to 4 1/2 years in prison for membership in a foreign terrorist organization. He now faces a second trial for involvement in torturing prisoners at an IS prison in Manbij. Prosecutors say that at least three prisoners died.