Federal and Mississippi state officials have closed the investigation into the 1964 killings of three civil rights volunteers by the Ku Klux Klan 52 years ago today. James Chaney, Andrew Goodman and Mickey Schwerner had traveled to Mississippi to register black voters. They disappeared while investigating the burning of a black church. Their bodies were found more than 40 days later in an earthen dam. While several people were convicted of civil rights violations in 1967, it took more than 40 years to bring the lead perpetrator in their murders to justice: Edgar Ray Killen, the only suspect ever tried for murder in the case, was convicted in 2005 and is serving a 60-year sentence. A Justice Department report released Monday names two men who may still be culpable in the murders, but the state said evidence has been “degraded by memory” and the case is closed.