Federal Bureau of Investigation (FBI) - established in 1908, and part of the Department of Justice. The FBI investigates most cases in which people are accused of violating federal criminal laws. After investigating these cases, the FBI pursues and arrest people suspected or charged with a federal crime. One of the most famous directors of the FBI was J. Edgar Hoover, who headed the Bureau from 1924 to 1972. Although he made many positive contributions to the FBI and to the nation, he also engaged in unethical behavior, such as wiretapping and maintaining files on individuals he did not like.