But the investigations will result in few indictments because decades have passed since the killings, making evidence gathering problematic, and some prime suspects have died, The Washington Post reported.
"There's maybe five to seven cases where we don't know who did it," FBI Special Agent Cynthia Deitle told the Post. Deitle is heading the bureau's effort. "Some we know; others we know but can't prove. For every other case, we got it."
The Post said at the least the project has solved some of the mystery surrounding the victims, many of whom were forgotten.
For example, the newspaper said, officials now believe an Alabama state trooper killed an unarmed civil rights protester in 1965. The case helped inspire the Rev. Martin Luther King Jr. to organize a march in the state.
The bureau determined in the cases of two North Carolina men who died in police custody -- one was found in 1956 with a crushed skull and the other refused medical treatment in 1960 after a heart attack -- there was no federal law it could use to pursue the cases.
In about one-fifth of the 108 cases, FBI investigators learned the deaths had no connection to the racial unrest in the South at the height of the civil rights fight.
In at least one case, the victim had been killed by a relative, but the family blamed the Ku Klux Klan.