And, nearly 50 years after Emmett Till’s mutilated body was found in a Mississippi river, federal investigators this week unearthed the Chicago teen’s casket in hopes of finding clues to a murder that helped kindle the civil rights movement. Mississippi prosecutors and the FBI have said DNA or other evidence might help determine who killed the 14-year-old and whether anyone still alive should be prosecuted. Two white men charged with the murder were acquitted by an all-white jury. The two, now dead, later confessed to beating and shooting Till, saying in a magazine article that they killed the teenager because he had whistled at one of their wives. The Justice Department announced plans last year to reopen the Till investigation.