I have the same issue. He's
SUPPOSED TO shoot himself (so I've read). The best Iv'e gotten was talking over the PA and a few seconds later an achievement (but the door was still locked). That was after quite a few tries. Even when I used C4 to give him a "helping hand" I just ended up failing. I did notice that he didn't have a gun on his person, in inventory or holstered on his side, so I shot him and he pulled a gun out but then he still didn't follow through. From my understanding this has been like this since the game's release and has yet to be fixed.