Members of Malcolm X’s family have made public what they described as a letter written by a deceased police officer stating that the New York Police Department (NYPD) and the Federal Bureau of Investigation (FBI) were behind the 1965 killing of the famed Black activist and civil rights advocate.

Malcolm X was a powerful orator who rose to prominence as the national spokesperson of the Nation of Islam, an African-American Muslim group that espoused Black separatism...