Dead of Night

Jack has just been acquitted of manslaughter, and regales his girlfriend Maggie and their neighbours with a disparaging account of the trial. According to the evidence (most of it Jack's), the victim, Philip Mercer, had broken in late at night, and, on being confronted by Jack, produced a gun which Jack got hold of during the ensuing struggle and then used to kill Mercer. A clear case of self-defence. Or was it?