Billy Wayne Posey, a key suspect in the murders of three civil-rights workers in 1964, died at age 73 on Thursday. Federal authorities say they will continue to investigate the Mississippi murders. The 1964 slayings of James Chaney, Andrew Goodman, and Michael Schwerner, who were in Mississippi to register black voters, shocked the nation and helped pass the Civil Rights Act of 1964. Hundreds of FBI agents investigated the men's disappearance, eventually finding them buried 15 feet below a dam. Seven people were convicted of trying to violate the victims' civil rights, and one man, a reputed Ku Klux Klan leader, was sentenced to 60 years in prison for manslaughter. Authorities say four suspects remain alive, and civil-rights activists have pressed for more murder convictions.