Willie Reed was 18 years old when he witnessed the murder of Emmett Till in Mississippi. Reed moved to Chicago after the trial.
He told prosecutors that he saw the two men charged with Till's murder driving a truck with the boy in the back, and then later heard screams coming from a nearby barn.
Despite fearing for his life, Reed came forward and testified at trial.
"He said even though he was scared, he had to testify, he had to tell what he saw," said Julie Louis, Willie Reed's wife.
When Willie Reed moved to Chicago, he changed his name to Willie Louis.
He was 76.
A memorial service is planned for Wednesday.