KOBLENZ, Germany—A former Syrian secret police officer was convicted by a German court Thursday of crimes against humanity for overseeing the abuse of detainees at a jail near Damascus a decade ago. Anwar Raslan is the highest-ranking Syrian official so far convicted of the charge. The verdict was keenly anticipated by those who suffered abuse or lost relatives at the hands of President Bashar Assad’s government in Syria’s long-running conflict. The Koblenz state court concluded that the defendant was in charge of interrogations at a facility in the Syrian city of Douma known as Al Khatib, or Branch 251, where suspected opposition protesters were detained. The court sentenced the 58-year-old to life in prison. His lawyers had asked judges last week to acquit their client, claiming that he never personally tortured anybody and that he defected in late 2012. “This day, this verdict is important for all Syrians who have …