BERLIN — A German court has convicted a Syrian refugee of being an accessory to a war crime against humanitarian operations over his participation in the 2013 kidnapping of a United Nations observer.

The Stuttgart state court Wednesday sentenced the defendant, who has been identified only as Suliman Al-S. in line with German privacy rules, to 3 ½ years in prison.

Prosecutors haven’t identified the observer but the facts released correspond with those of the kidnapping of Canadian lawyer Carl Campeau, who was abducted from a Damascus suburb. He escaped after eight months.

The court found the defendant backed the kidnapping and offered to serve as a guard, but didn’t find conclusive proof that the Nusra Front, al-Qaida’s branch in Syria, was behind the kidnapping or that the defendant belonged to it.