It was an act of "pure, pure concentrated evil", Charleston's mayor said - a black community's leading lights extinguished at the hands of a young white man, who was welcomed into their Bible study session.
In one blow, the gunman ripped out part of South Carolina's civic heart.
A state senator who doubled as the church's minister, three other pastors, a regional library manager, a high school coach and speech therapist, a government administrator, a college enrolment counsellor and a recent college graduate.
Six women and three men who felt called to open their church to all.
Dylann Storm Roof, 21, had complained that "blacks were taking over the world" and that "someone needed to do something about it for the white race", according to a friend who alerted the FBI.
US President Barack Obama called the tragedy yet another example of damage wreaked on America by guns.
Head of the National Association for the Advancement of Colored People, Cornell William Brooks, said "there is no greater coward than a criminal who enters a house of God and slaughters innocent people".
Others bemoaned the loss to a church that has served as a bastion of black power for 200 years, despite efforts by white supremacists to wipe it out.
"Of all cities, in Charleston, to have a horrible hateful person go into the church and kill people there to pray and worship with each other is something that is beyond any comprehension and is not explained," said Mayor Joseph Riley Jr.
Surveillance video showed the gunman entering the church on Wednesday night, and Charleston County Coroner Rae Wilson said the gunman initially didn't appear threatening.
"The suspect entered the group and was accepted by them, as they believed that he wanted to join them in this Bible study," she said.
"(Then) he became very aggressive and violent."
Roof's childhood friend, Joey Meek, called the FBI after recognising him in the surveillance footage.
"I didn't think it was him. I knew it was him," Meek told The Associated Press after being interviewed by investigators.
Roof was arrested 400 kilometres away in Shelby, North Carolina, after a motorist spotted him and tipped-off police.
He has been transferred back to South Carolina, and will be held in a Charleston detention centre pending a bond hearing.
Spilling blood inside "Mother Emanuel", founded in 1816, evoked painful memories across the United States, a reminder that black churches so often have been the targets of racist violence.
US Attorney General Loretta Lynch said the attack would be investigated as a hate crime.
Meanwhile, Obama, who personally knew the lead pastor Clementa Pinckney, was one of the few politicians to call for stricter gun control.
"I've had to make statements like this too many times," the president said.
"At some point, we as a country will have to reckon with the fact that this type of mass violence does not happen in other advanced countries."
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