Mary Bell:
// On 25 May 1968, the day before her 11th birthday, Mary Bell strangled four-year-old Martin Brown in a derelict house.[1] She was believed to have committed this crime alone. Between that time and a second killing, she and a friend, Norma Joyce Bell (no relation), aged 13, broke into and vandalised a nursery in Scotswood, leaving notes that claimed responsibility for the killing. The police dismissed this incident as a prank.
On 31 July 1968, the pair took part in the death, again by strangling, of three-year-old Brian Howe, on wasteland in the same Scotswood area.[1] Police reports concluded that Mary Bell had later returned to his body to carve an "N" into his stomach with a razor; this was then changed using the same razor but with a different hand to an "M". Mary Bell also used a pair of scissors to cut off some of Howe's hair, scratch his legs, and mutilate his penis. //
Or the Bulger killers.
These incidents are very rare, but they are nothing new. Each generation seems to throw one up.