The first, and still best-known, example of the "serial killer" - a term coined by an FBI agent in the 1970s - was Jack the Ripper who murdered five prostitutes in the Whitechapel area of east London in 1888.
If the 12 killings in the Cromwell Street "house of horror" and elsewhere in Gloucestershire were the work of one person, the murderer would take a place halfway up the "league table", above John Christie and Ian Brady, and just below the Yorkshire Ripper, Peter Sutcliffe.
1. MARY ANN COTTON: 20 or more victims. She married three times and in 20 years poisoned husbands, children, step-children, other relatives and friends with arsenic. Motive - insurance money, remarriage or sheer spite. Hanged in 1873.
2. DENNIS NILSEN: 16 victims. He strangled young men "for company" at his home in Muswell Hill, north London, keeping their bodies under the floorboards and bringing them out to watch television. Jailed for life in 1983.
3. MICHAEL RYAN: 16. Gun-club enthusiast who went on a one-hour rampage through Hungerford, Berkshire, in 1987, firing119 shots with a Kalashnikov rifle and a pistol. Shot himself dead after being surrounded by police.
4. BRUCE LEE: 15. The 20-year-old arsonist started a series of fires in Humberside. He was convicted of 26 murders, but the number was reduced to 15 on appeal. Detained for life in 1977.
5. PETER SUTCLIFFE: 13. Known as the Yorkshire Ripper, Sutcliffe preyed on prostitutes and young women, mainly in the Leeds area. Detained for life in 1981 and sent to Broadmoor high security mental hospital.
6. IAN BRADY: 10. A decade after he was jailed for the Moors murders with accomplice Myra Hindley, Brady admitted killing another five people, bringing the total number of his victims to 10. Jailed for life in 1966.
7. JOHN HAIGH: 9. Disposed of his victims - wealthy widows from whom he had conned money - by immersing their bodies in a 40-gallon drum of acid. Haigh boasted that there was no evidence, but a forensic scientist found one plastic denture which survived the acid. Hanged in 1949.
8 JOHN CHRISTIE: 8. He gassed, strangled and raped six women. At 10 Rillington Place in London's Ladbroke Grove, he is also believed to have killed the wife and child of his tenant Timothy Evans. Christie was hanged in 1953.
9 KENNETH ERSKINE: 7. Known as the Stockwell Strangler, all his victims were frail pensioners. After throttling them, he would clean their homes and leave the bodies lying in bed with sheets pulled up to the chin. Jailed for 40 years in 1988.
10 JOHN CHILDS: 6. Victims were killed for cash, dismembered and burned in the grate of Childs's flat in Poplar, east London. He carried out two of the contract killings dressed all in black, complete with an undertaker's hat. He was jailed for life in 1980.
11 COLIN IRELAND: 5. Victims died because Ireland, an unemployed drifter, wanted to make his mark in life. He targeted homosexual men who indulged in sado-masochism and killed them in their own homes after deliberately setting out to be classed as a serial killer. Jailed for life in 1993.
Since Jack The Ripper, criminologists say there have been roughly 100 known cases of serial killers around the world, including Pedro Lopez, the "Monster of the Andes", who confessed to killing 360 pre-teenage girls in Bolivia in the 1970s.
The world's most prolific murderer was an Indian, Behram, who strangled 931 people with a yellow and white cloth between 1790 and 1840.