On April 4, 1968, the Rev. Martin Luther King Jr., 39, was shot to death as he stood on a balcony of the Lorraine Motel in Memphis, Tenn.; the killing sparked a wave of riots across the U.S. (James Earl Ray later pleaded guilty to assassinating King, then spent the rest of his life claiming his innocence and attempting to withdraw his guilty plea; he died in prison in 1998.)