Four Klansmen were identified as suspects within days of the 1963 bombing of the Sixteenth Street Baptist Church in Birmingham which killed four black girls.
Thomas Blanton Jr., 62, was sentenced to life in prison by the same jury that found him guilty of murder Tuesday.
Another former Klan member, Robert "Dynamite Bob" Chambliss, was convicted of murder in 1977 and died in prison in 1985, always maintaining his innocence.
Former Klansman Bobby Frank Cherry was indicted last year but his trial was delayed after questions arose about his mental competency.
A fourth suspect, Herman Cash, died without being charged.