Mary's mother, Betty Bell, was a prostitute who often went to Glasgow on "business". She was also a disciplinarian. Mary had a bedwetting problem and when she wet her bed her mother would rub her face in the urine and then hang the mattress up for the entire neighbourhood to view.
Mary's father's name was Billy Bell and, although he wasn't her biological father, she saw him as one. She loved him but he was not a good role model. He was a thief who was later convicted of armed robbery.
She strangled two children, killing toddler Martin Brown, her first victim, when she was 10 years old. She later killed three-year-old Brian Howe. She and her friend, Norma, used scissors and razor to cut marks into Howe's dead body. Mary Bell was convicted of manslaughter in 1968. She was released from prison in 1980 and was granted anonymity to start a new life (under an assumed name) with her daughter. This daughter did not know of her mother's past until Mary Bell's location was discovered by reporters. The daughter's anonymity was originally protected until she reached the age of 18.
She is the subject of an in-depth, serious (and not salacious) biography, Cries Unheard: the Story of Mary Bell by Gitta Sereny (Macmillan, London, 1998. Hardback ISBN: 0333735242; paperback ISBN: 0333753119). This details the fact that Bell herself was the victim of abuse. The book was criticised strongly by the media, particlularly the tabloid press, and by the government, but in a 1999 debate in the House of Lords, Lord Wakeham stated "the public interest oozes from every pore of the book".