A. A is liable because he has failed to make reasonable inquiries which must have elicited the true facts whether Z was a murderer or acting in self-defence.
B. A is liable for wrongfully apprehending Z because Z was acting in self-defence.
C. A is liable because he was neither bound by law nor justified by law to apprehend Z on a simple belief that Z was a murderer.
D. A has committed no offence because he is entitled to the defence of mistake of fact under section 79 of the Penal Code.
✅ The correct answer is option D.