When 32-year-old Marlene Doyle, reported missing by her mother, is found murdered in a Coventry flat, police turn to forensic evidence to identify her killer.

West Midlands Police work with ballistics experts to find out whether a man with a haul of rifles in his bedroom has used a 3D printer to make potentially deadly weapons.

A man rings 999 to say he has killed his flatmate and forensics officers search for clues that could prove or disprove the suspect's pleas of self-defence.