In a videotaped confession shown Friday during his death penalty trial, Roof laughed several times and made exaggerated gun motions as he recounted the massacre. He explained that he wanted to leave at least one person alive to tell what happened and complained that his victims "complicated things" when they hid under tables.
Forty-five minutes into the interview, an FBI agent decided to tell him nine people died in the June 17, 2015, shootings at Emanuel African Methodist Episcopal Church.
"There wasn't even that many people in there," Roof said incredulously. "Are you lying to me?"
The blurry video made it hard to see his face. After being told the details, an agent asked how he felt.
"Well, it makes me feel bad," said Roof, who earlier in the confession estimated he might have killed five.
Roof's lawyers have conceded that he carried out the attack and are concentrating on convincing jurors to spare his life in the second phase of the trial.
Later Friday, Roof's handwritten journal was read aloud. It was full of dubious, offensive racial claims about blacks and Jews, from stories about African-Americans enjoying slavery to segregation keeping white people from being dragged down.
"How could our faces, skin color and body structure be so different, but our brains exactly the same?" Roof wrote.
His video confession came about 17 hours after the shooting. FBI agents drove to Shelby, North Carolina, where he was arrested. The plane that would take him back to Charleston was not going to arrive for a few hours. So FBI agent Michael Stansbury got permission to take a chance and interview him immediately.
It paid off. After reading Roof his rights and engaging in brief small talk, an agent asked Roof what he was doing on the night of the killings.
"I went to that church in Charleston and, uh, I did it," he said.
Roof said he wanted to kill black people because they rape white women daily. Agents asked why he chose Emanuel AME. He said online it was listed as the oldest black church in the South, and there probably would not be any white people there.
"I knew that would be a place to get a small amount of black people in one area," Roof said, later adding, "They're in church, they weren't criminals or anything."
Earlier testimony from survivor Felicia Sanders said Roof sat through the Bible study beside pastor Clementa Pinckney and opened fire as the rest of the group of 12 closed their eyes for a final prayer.
"I was sitting there thinking about whether I should do it or not. That's why I sat there for 15 minutes. I could have walked out," Roof said.
Church surveillance videos indicate Roof was actually inside for about 45 minutes.
Roof, as he has for much of the trial, hardly looked up as the confession played, mostly just shuffling papers in front of him.
He told FBI agents questioning him that he could never look at the families of the victims. And throughout the trial, he has not looked at the dozens of family members in the courtroom.
Roof meticulously prepared for the shootings. He carried eight magazines that could each hold 13 bullets. But he only loaded 11 bullets so he could shoot 88 times — a revered number among white supremacists, standing for Heil Hitler because H is the eighth letter of the alphabet.
In the confession, Roof said he left bullets in a magazine so that he could kill himself after the slayings but changed his mind when he didn't immediately see any police.
At one point, an agent asked if Roof thought about killing more blacks.
"Oh no. I was worn out," Roof said.
A crime scene technician testified that she found two handwritten notes in Roof's car — one to his mother and one to his father. He told his dad: "I love you and I am sorry. You were a good dad."
To his mother, he said: "As childish as it sounds, I wish I was in your arms."
Roof's mother suffered a heart attack while watching opening statements Wednesday. Her condition is unclear.
Roof said the killing of Trayvon Martin was a turning point in his life. Martin, a young unarmed black man, was killed by neighborhood watch volunteer George Zimmerman in 2012. Zimmerman was acquitted in the shooting. Roof said he started researching black crime against whites on the internet.
He told the agents he didn't talk about his racist beliefs with his friends or family.
"They probably won't agree with me — you know what I'm saying?"
Follow Jeffrey Collins on Twitter at http://twitter.com/JSCollinsAP. His work can be found at http://bigstory.ap.org/content/jeffrey-collins.
An earlier version of this story incorrectly said the shooting happened last June. It happened in June 2015.
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