World's Most Evil Killers säsong 4

Having murdered an estimated 250 people, Harold Shipman became one of the most prolific serial killers in history when he targeted vulnerable patients, yet the once-trusted doctor never revealed his motives.

Known to some as 'The Plumstead Ripper', rapist Robert Napper found himself convicted of two brutal murders, but the number of victims targeted by him may have actually been much higher.

The life and crimes of the convicted fraudster Stephen Seddon, a murderer driven by greed who killed his parents in cold blood when his attempt to fake a car accident ended in failure.

Profiling 29-year-old Dale Cregan, who was sentenced to life in prison after he went on a ruthless killing spree, murdering two men and two police officers in gun and grenade attacks in 2012.

The brutal murder of a disabled man led police to 21-year-old Anthony Arkwright, a habitual local criminal who killed four people during a horrific spree that lasted 56 hours in 1988.

A profile of the cold-blooded killer John Sweeney, finally convicted in 2011 of the horrific murders of two former girlfriends whom he had left in the canals of London and Rotterdam.

Dubbed 'The Beast of Mława', Andrezej Kunowski had a long history of sexual violence in Poland before he moved to London, where he murdered 12-year-old Katerina Koneva and may have killed others.

In 1983, Arthur Hutchinson took the lives of three members of the Laitner family after breaking into their South Yorkshire home, but the police eventually caught up with the murderer.

In December 1995, serial killer Peter Moore was charged with the murder of four men in North Wales, admitting to nearly 50 violent and brutal attacks on defenceless men between 1975 and 1995.

Andrew Dawson was given a second life sentence for the unprovoked murders of his two neighbours while he was out on release from prison for the killing of a 91-year-old man in 1982.