June 2 (UPI) -- Missing American journalist Austin Tice was imprisoned by the regime of the since-deposed Syrian President Bashar al- Assad in 2012 with his whereabouts now not known, according to top secret intelligence files uncovered by the BBC. Former Syrian officials also have confirmed Tice's detention to the BBC . The material was part of a BBC investigation more than one year ago for a Radio 4 podcast series in accompanying a Syrian investigator to an intelligence facility. The Assad