On Sept. 15, 1963, a bomb went off at the Sixteenth Street Baptist Church in Birmingham, Ala., killing Denise McNair, 11, and Addie Mae Collins, Carole Robertson and Cynthia Wesley, all 14. It was a Sunday morning, and the four girls, dressed in white, were in the church basement, preparing to attend Sunday school and the monthly Youth Day service. As the panicked survivors fled from the explosion and police and ambulances arrived, the man convicted of the crime years later stood across the street enjoying the commotion.
In his documentary 4 Little Girls, which debuts on HBO on Feb. 23...