-- Nearly 50 years after Emmett Till's mutilated body was found in a river in Mississippi, federal investigators unearthed the Chicago teenager's casket Wednesday in hopes of finding clues to a killing that helped kindle the civil rights movement.

Mississippi prosecutors and the FBI have said DNA or other evidence may help determine who killed the black 14-year-old and whether anyone still alive should be prosecuted.

Fishermen found Till's body in the Tallahatchie River in August 1955, three days after he was abducted from his uncle's home in Money, Miss., reportedly for whistling at a white woman.

FBI agents loaded the concrete vault containing Till's casket onto a flatbed truck Wednesday and hauled it from a suburban cemetery to the Cook County medical examiner's office in Chicago for an autopsy. None was ever performed.

Investigators hope to determine the cause of Till's death and to "see if any further evidence can be looked at to help Mississippi officials bring additional charges if warranted," FBI spokesman Frank Bochte said.

Two white men charged with killing Till -- store owner Roy Bryant and his half-brother J.W. Milam -- were acquitted by an all-white jury. The two, now dead, later confessed to beating and shooting Till, saying in a Look magazine article that they killed the teenager because he had whistled at Bryant's wife.

During the trial, defense attorneys suggested the body was not Till's and that the boy was alive.

Simeon Wright, a cousin who was with Till the night he was abducted, said he hopes the autopsy will dispel that notion.

Wright and two other relatives held a graveside prayer service before the casket was dug up. The body is to be returned to the grave within a week, officials said.

A vault containing the casket of Emmett Till is loaded onto a truck at the Burr Oak Cemetery in Alsip, Ill.