Nilsen murdered 15 young men whose bodies he sought to preserve as companions before dismembering their remains for disposal down the toilet.
Few killers have divided opinion like Aileen Wuornos. Having gunned down six people, she confessed, but it was not enough to save her.
Two British serial murderers killed a generation apart, but with a common goal - they killed to gain an infamy that had eluded them in normal life.
Pickton was a pig farmer who killed 49 women before feeding them to his hogs. He was caught when an undercover police officer posed as a cellmate.
Ridgway remains one of the most prolific murderers in U.S. history, even killing prostitutes while his young son waited in the back of his car.