Nine people were killed at a historic black church in South Carolina in 2015

In 2015, a white gunman killed nine black parishioners at a historic black church in downtown Charleston, S.C.

Dylann S. Roof, a self-radicalized white supremacist, confessed to the killings.

Mr. Roof, then 21, entered through an unlocked side door of the Emanuel African Methodist Episcopal Church and took a seat at a weekly Bible study meeting. He had brought with him a semiautomatic pistol that he concealed in a pack on his waist.

When the congregants closed their eyes for a familiar benediction, the sound of gunfire roared through the fellowship hall. Churchgoers dove below tables but Mr. Roof kept firing, striking the victims at least 60 times.

Mr. Roof was charged with 33 counts, including hate crimes resulting in death. He was found guilty in 2016 and sentenced to death last year.

At Emanuel A.M.E. Church, a bedrock of black Charleston that was founded in 1791, doors that were once left open have had to be locked since the shooting. The church has used retired military and on- and off-duty police officers for security.

Willi Glee, a member of the church, said last year that religious spaces offer an added attraction for some attacks because defiling them is the ultimate taboo. “Everybody expects that a house of worship is a safe place,” he said.