Updated: 19 Apr 2021, 11:56 Invalid Date, LAST night's incredible episode of Line of Duty had fans on the edge of their seats - but left us with even more unanswered questions. 5 Could James Nesbitt's corrupt DCI Thurwell, who is retired in Spain, be H? And suspicion was immediately raised that DCI Thurwell, who was first mentioned in series three of the cop drama, could be H. He was the senior investigating officer (SIO) on the probe into the death of social worker Oliver Stephens-Lloyd - the social worker who reported claims of sexual abuse at Sands View Boys' Home. Stephens-Lloyd's death was originally ruled as suicide by DCI Thurwell's team - but when AC-12 dug deeper, they found that the social worker was murdered.