Anatoly Slivko was a respected Soviet youth-club leader who concealed a series of murders of boys over two decades before his arrest in 1985.

Amy Archer-Gilligan ran a Connecticut nursing home where she poisoned residents for profit, a case that helped inspire the play 'Arsenic and Old Lace'.

Helene Jegado, a French domestic servant, is believed to have poisoned dozens of people with arsenic over nearly two decades before her execution in 1852.

Enriqueta Marti, the 'Vampire of Barcelona', became infamous in 1912 amid claims of child kidnapping, in a case where fact and sensation are hard to separate.

Robert Maudsley, one of Britain's most isolated prisoners, killed four people and has spent decades in a specially built solitary cell.

Donald Neilson, the 'Black Panther', murdered three sub-postmasters and kidnapped heiress Lesley Whittle in a case that gripped 1970s Britain.

Mary Ann Cotton, one of Britain's most prolific poisoners, is believed to have killed around 21 people with arsenic before her execution in 1873.

Velma Barfield, the 'Death Row Granny', was the first woman executed in the US after the reinstatement of capital punishment, convicted of fatal poisonings.

William Heirens, known as the 'Lipstick Killer', confessed to 1940s Chicago murders in a contested case that became one of America's longest imprisonments.

Jack Unterweger was an Austrian who became a celebrated writer after a murder conviction, then killed again across two continents once released.

Peter Manuel, the 'Beast of Birkenshaw', was one of Scotland's most notorious killers, convicted of seven murders before his execution in 1958.

Stephen Port, the London 'Grindr Killer', murdered four young men he met through dating apps, and the flawed police response triggered a major inquiry.

Peter Tobin, a Scottish killer convicted of three murders, was the subject of Operation Anagram, a nationwide effort to trace his decades of movements.

John George Haigh, Britain's 'Acid Bath Murderer', killed for profit in the 1940s and wrongly believed that destroying the bodies meant he could not be convicted.

Jerry Brudos, the Oregon 'Lust Killer', murdered young women in the late 1960s, his crimes driven by disturbing fixations traced back to childhood.

Ángel Maturino Reséndiz, the 'Railroad Killer', used America's freight network to murder across several states before his 1999 surrender.

Beverley Allitt, a British nurse called the 'Angel of Death', attacked children in her care in 1991, a case linked to the rare Munchausen syndrome by proxy.

Leonarda Cianciulli, the Italian 'Soap-Maker of Correggio', killed three women between 1939 and 1940, driven by a tragic web of superstition.

Tommy Lynn Sells, a drifter who claimed dozens of murders, was stopped when a brave 10-year-old survived his attack and identified him. He was executed in 2014.

Thierry Paulin, the 'Monster of Montmartre', murdered up to 21 elderly women in 1980s Paris with an accomplice — but died of AIDS before he could ever face trial.