BIRMINGHAM, Ala. (AP) — Alabama on Friday will mark the 60th anniversary of one of the most heinous attacks during the Civil Rights Movement, the 1963 bombing of a church that killed four Black girls in 1963.

U.S. Supreme Court Justice Ketanji Brown Jackson, the first Black woman on the nation’s highest court, will give the keynote address at the remembrance Friday morning at 16th Street Baptist Church in Birmingham.

On the morning of Sept. 15, 1963, dynamite planted by Ku Klux Klan members exploded at the church, killing the girls and shocking the nation. The large, prominent church was targeted because it was a center of the African American community and the site of mass meetings during the Civil Rights Movement.

The girls were gathered in a downstairs washroom to freshen up before Sunday services when the blast rocked the church. The explosion killed 11-year-old Denise McNair, and Cynthia Wesley, Carole Robertson, and Addie Mae Collins, all 14. A fifth girl, Sarah Collins Rudolph, the sister of Addie Mae, was in the room and was severely injured but survived.

The racist attack came eight months after then-Gov. George Wallace pledged, “segregation forever” during his inaugural address and two weeks after the Rev. Martin Luther King Jr. delivered his iconic “I Have a Dream” speech in Washington.

Lisa McNair, Denise’s sister, said as the nation remembers the 60th anniversary, she wants people to remember what happened and think about how they can prevent it from happening again.

“People killed my sister just because of the color of her skin,” McNair said. “Don’t look at this anniversary as just another day. But what are we each going to do as an individuals to try to make sure that this doesn’t happen again,” McNair said.

Three Ku Klux Klansmen were eventually convicted in the blast: Robert Chambliss in 1977; Thomas Blanton in 2001; and Bobby Frank Cherry in 2002.

A wreath will be laid at the spot where the dynamite device was placed along an outside wall. McNair has asked city churches to join in tolling their bells Friday morning to mark the moment when the bomb went off.