Sereny, Gitta. Cries Unheard -- Why Children Kill: The Story of Mary Bell. New York: Metropolitan Books, 1999.
Sereny Gitta. The Case of Mary Bell. London: Arrow Books, 1972. (Out of print)
For news on the furor caused by the publication of Cries Unheard, and Mary Bell's payment for her participation, the UK News Electronic Telegraph is the best online source, particularly issues dated between April 27, 1988 and June 17, 1988. For specific issues with articles on Mary Bell, see issues #1067, 1070, 1071, 1072, 1074, 1079, 1086, 1118.