Mary Flora Bell (born on May 26 1957 in Newcastle upon Tyne, England) was convicted in December 1968 of the manslaughter of two boys, Martin Brown (four years old) and Brian Howe (three years old). Bell was eleven years old at the time of the killings.
Mary Bell was convicted of strangling a young boy, Martin Brown, on May 25, 1968, the day before her 11th birthday. She was, as far as anyone knows, alone on this occasion. Between that time and the second killing, she and her friend Norma Bell (who was not related to her) broke into and vandalised a nursery in Scotswood, leaving notes that claimed responsibility for the Brown killing. The Newcastle Police dismissed this incident as a prank.On July 31, 1968, the two took part in the death, again by strangulation, of three-year-old Brian Howe. Police reports concluded that Mary Bell had gone back after killing him to carve an "N" into his stomach with a razor; this was then changed using the same razor but with a different
Source: http://en.wikipedia.org/wiki/Mary Bell