Fares A.B., whose last name wasn't released for privacy reasons, is also charged with war crimes and violations against the war weapons control act, prosecutors said Wednesday.
They said in 2012 he first joined a local branch of the Free Syria Army and shot two prisoners.
In 2014, he joined the Islamic State and participated in the mistreatment of three prisoners in Syria. He also took several people prisoner and abused the driver of a pickup during a vehicle inspection by beating his machine gun against the man's head. Later in 2014, he participated in the execution of a prisoner.
Prosecutors didn't say when the Syrian arrived in Germany, but said he is already imprisoned for another crime.