Spanning across decades, unsuspecting patients of Harold Shipman would visit his medical centre. While they attended for regular check-ups or do have ailments fixed, they instead had their bodies flooded with a drug overdose. Shipman is believed to be Britain's most prolific serial killer - despite working in a profession where he'd be expected to make people feel better. 

What does it take for a killer like this to start striking? Listen to today's episode to learn more about one of Britain's most notorious killers.