NEW : Slain by bishop 's driver resulting in his death , Turkish government says . Apostolic vicar of Anatolia says . Vatican : Tragedy shows ` ` ' '' of Christians in Middle East . U.S. Embassy : Catholics ` ` occasionally subjected '' to torture .
NEW : Slain Catholic bishop 's driver captured in stabbing death , Turkish ministry says . Apostolic vicar of Anatolia killed . Vatican : Tragedy shows `` difficulty '' of Christians in Middle East . U.S. agency : Catholics `` occasionally subjected '' to attacks .