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Joe Navarro, a former FBI criminal profiler and veteran counterterrorist agent, recently penned an article for Psychology Today in which he reverse engineered the psyches of past killers.
He argues that Roof's overtly racist motives and heroic visions of grandeur put him squarely in two familiar camps of killers: the paranoid and the narcissistic.
"We don't know a lot about him just yet," Navarro tells Business Insider. "But we definitely would put him first in the paranoia box."
Paranoia in this sense refers to a deeper and more irrational fear than the mild type of worry that strikes when you think you left the oven on. It refers to the constant fear that others want to hurt, kill, and destroy you.
Just recently, investigators discovered an online manifesto that they believe was written by Roof. The excerpts detail the author's beliefs that blacks are "stupid and violent" with "the capacity to be very slick," the New York Times reports. It expresses regret over white flight, instead arguing whites should have stuck around the cities to fight.
Paranoid people tend to "collect wounds," as Navarro puts it. They sort through history and mine it for every instance in which a group of people - in Roof's case, whites - has been wronged. Then, they use that as justification for a heinous act.
"What happens is, with paranoid ideation, the only way they see how to fix things is through violence," Navarro says.
With an imminent threat looming and all the evidence at their disposal suggesting the need for massive action, paranoid people assume responsibility for eliminating the perceived threat.
Enter trait two: narcissism.
"I'm not talking about the narcissism that would make you label a hotel chain after yourself," Navarro says. "I'm talking about narcissism where even though you lead a rather unfulfilled life you still see yourself as superior and somebody else as inferior."
That could explain why so many mass murders are committed by lone gunmen.
In their eyes, they aren't just killing a group of people; they're standing up for an entire ideology. They see one group of people as a force of evil and themselves not just as a force of good, but the only force of good qualified to get the job done.
After killing nine of the 12 members of the prayer group, Roof turned to an elderly woman named Sylvia Johnson, who later recalled that Roof asked her if she had been shot. She said no.
"And he said, 'Good, because we need a survivor because I'm going to kill myself,'" Johnson told CNN.
According to Navarro, killers want recognition for their brutal crime as if they are performing a heroic deed. Because in their eyes, that's exactly what they're doing.
"When you have this toxic combination of narcissism and paranoia, you can do anything because you're justified," Navarro says. "You fear something, you hate something, and you feel like you're entitled to deal with it by whatever means you want."