CHARLESTON, S.C. -- Prosecutors are using Charleston church shooter Dylann Roof’s own words to portray him as a cruel angry racist at his death penalty trial.

Roof’s two-hour confession on video to killing nine people at a church Bible study, recorded the day after the shooting, was introduced as evidence Friday, along with a handwritten journal found in his car.

“How could our faces, skin color and body structure be so different, but our brains exactly the same?” Roof wrote in one of the less offensive passages.

In the video, Roof laughed repeatedly and made exaggerated gun motions as he described the massacre. He wanted to leave at least one person alive to tell what happened, he explained, complaining that his victims “complicated things” by hiding under tables.

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He thought about shooting drug dealers, but they might shoot back, he said. Instead, Roof told the FBI, he picked the historic Emanuel African Methodist Episcopal Church in June 2015 because there likely wouldn’t be white people there, and the people he chose to slaughter were more likely to be meek.

“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.”

Surveillance video from the day of the attack in June 2015 showed people walking into the church. Then, in walks Roof, carrying a 45 Glock pistol and seven magazines. Once inside, he opened fire as the faithful rose and closed their eyes to pray.

Malcolm Graham, whose 54-year-old sister Cynthia Hurd was murdered, spoke to CBS News.

“This was an attack on a race of people and an attack on the Christian church and an attack on humanity,” Graham said.

In Roof’s confession video, an FBI agent asked Roof, “Why did you do it?”

“I had to do it because somebody had to,” Roof said. “Blacks are raping and killing white people on the streets every day... What I did is still minuscule to what they’re doing to white people every day.”

Roof’s lawyers have conceded that he carried out the attack, and are focused on persuading jurors to spare his life in the penalty phase of the trial. They said in opening statements they will call few or no witnesses. Testimony continues next week, and prosecutors said they may rest their case Wednesday.

Along with the overt racism, Roof’s confession and notes show the then-21-year-old as naive and immature. He wrote a note apologizing to his mother and saying “as childish as it sounds, I wish I was in your arms.”

But Roof meticulously prepared for the shootings. He carried eight magazines that could each hold 13 rounds, but loaded only 11 each so that he could shoot 88 times. That’s a revered number among white supremacists, standing for “Heil Hitler” because H is the eighth letter of the alphabet.

At one point, an agent asked if Roof had thought about killing more blacks.

“Oh, no. I was worn out,” Roof said.

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.

He apparently hadn’t heard the news during his 17 hours on the run. About 45 minutes into his interview with the FBI, an agent decided to tell him that nine people were dead.

“There wasn’t even that many people in there,” Roof said incredulously. “Are you lying to me?”

The video is blurry, making it hard to see Roof’s facial expressions. 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.

Agents asked Roof why he chose Emanuel AME. He said it’s because he saw it described online as the oldest black church in the South.

Survivor Felicia Sanders testified that 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 also 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?”

Roof hardly looked up as his confession played, mostly shuffling papers in front of him, as he has through much of the trial.

In the recording, he told FBI agents he could never look at the families of his victims. And throughout the trial, he has not looked at the dozens of relatives in the courtroom.