In the early morning of Sunday, September 15, 1963, Bobby Frank Cherry, Thomas Blanton, Herman Frank Cash, and Robert Chambliss, members of United Klans of America, a Ku Klux Klan group, planted a box of dynamite with a time delay under the steps of the church, near the basement.
At about 10:22 a.m., when twenty-six children were walking into the basement assembly room for closing prayers of a sermon entitled “The Love That Forgives,” the bomb exploded. According to an interview on NPR on September 15, 2008, Denise McNair's father stated that the sermon never took place because of the bombing. Four girls, Addie Mae Collins (aged 14), Denise McNair (aged 11), Carole Robertson (aged 14), and Cynthia Wesley (aged 14), were killed in the attack, and 22 additional people were injured, one of whom was Addie Mae Collins' younger sister, Sarah.
The explosion blew a hole in the church's rear wall, destroyed the back steps, and left intact only the frames of all but one stained-glass window. The lone window that survived the concussion was one in which Jesus Christ was depicted knocking on a door, although Christ's face was destroyed. In addition, five cars behind the church were damaged, two of which were destroyed, while windows in the laundromat across the street were blown out.