10 of the World's Most Prolific Serial Killers

Harold Shipman
A family plays behind the new Garden of Tranquility in Hyde Park, Greater Manchester, England, which commemorates those who died at the hands of mass murderer Dr. Harold Shipman. PHIL NOBLE/AFP/Getty Images

Harold Shipman was a trusted, respected physician in England who treated more than 3,000 patients in his career. But underneath that conventional image, the father of four was a drug addict with multiple convictions, who somehow managed to keep practicing medicine.

Shipman also harbored a secret urge to kill women, which he satisfied by making house calls to elderly female patients and giving them lethal injections of the opiate diamorphine. Most of his victims were found sitting in their living rooms, as if they had died quietly of natural causes. After authorities grew suspicious and exhumed bodies to test them, Shipman was arrested in 1998. Two years later, a British court convicted him of 15 murders, making him the most prolific serial killer in that nation's history. But a later investigation linked him to a total of 215 deaths [source: BBC News, Hoge].

Why he killed so many people remains a mystery. Prosecutors portrayed him as an arrogant man who considered himself intellectually superior to others, and who reveled in the sense of power that he got from taking lives. "He was very definitely not doing it for excitement, far from it," said forensic psychologist Dr. Richard Badcock in a BBC report. "He was doing it mainly to try and resolve something within himself ... to get rid of an anxiety but an anxiety which he might not even have let himself think about" [source: BBC News, Hoge].

In 2004, Shipman hanged himself in his jail cell [source: BBC News].