The age of criminal responsibility was determined by MPs in the 1963 Children and Young Persons' Act. Children aged 10 were judged to be able to know the consequences of their actions. Previously the age in England and Wales was eight. Below 10, the law considers children to be unaware of the consequences.
Mary Bell secured her unhappy place in the murderers' Who's Who when she strangled four- year-old Martin Brown in a derelict house close to her home in the Scotswood district of Newcastle- upon-Tyne.
Two months later, in July 1968, the body of three-year-old Brian Howe was found on waste ground in the same area. He too had been strangled.
Police questioned more than 1,200 children about both deaths, eager to find the author of four notes in a child's handwriting that had been discovered after a break- in at a school. One of the notes referred to Martin's death.
Bell quickly fell under suspicion after changing her account of her whereabouts twice. In her school book, police found a picture she had drawn of the outstretched body of a child lying on the floor of a room under a window - matching the scene where Martin's body had been found.
A 13-year-old neighbour of Bell was also suspected of some involvement. After more questioning, mutual accusations of guilt flew between them.
Both stood trial for murder at Newcastle Assizes in December 1968. One account said Bell seemed unperturbed at her predicament, with an 'adult grasp of the complex proceedings' while demonstrating a 'guile and understanding well beyond her years'.
In the second week of her trial, Bell's co-accused was found not guilty of murder and released. The jury found Bell guilty of manslaughter on the grounds of diminished responsibility. Mr Justice Cusack ordered she be 'detained indefinitely At Her Majesty's Pleasure'.
During the trial, the judge remarked to the jury that the legal system was not equipped to deal with cases like those of Mary Bell.
As no psychiatric hospital could be found to take her, she spent the first six years of her detention in a special unit of an approved school for boys.
At 17 she was transferred to Styal prison in Cheshire and then to an open prison in Staffordshire.
In 1977, aged 20, she absconded for three days. On recapture, she told police and prison officers she wanted to prove she could live a normal life. Two years later, shortly before her 23rd birthday, she was released on licence.
During 12 years of her detention she reportedly received no psychiatric treatment although it was recommended. When she was released she adopted a new identity and took court action to prevent details of her new life becoming public.Reuse content