Vester Flanagan was determined to explain himself. After murdering two TV journalists (and former coworkers) during a live broadcast in Virginia on Wednesday, he faxed three different suicide notes to ABC News that were strewn with absurdities, contradictions, and baffling rationalizations. Flanagan, who was black and went by the name Bryce Williams on air, complained about racism against him at the TV station, WDBJ, but then confessed to acting "somewhat racist against whites, blacks and Latinos" himself. He admitted to killing his own cats—because he was fired unfairly. He said how much he loved them, then gave a long, sadistic account of the execution; he killed his favorite first, and she didn't go quickly. Then he described the extreme trauma on the second cat's face as he killed her. He called it a gruesome scene—then decided he owed them a decent burial. Through the rambling diatribe, victimization is a constant theme: "Haters" hounding, demeaning, and harassing him at every turn. "I have a right to be outraged!!!”

Before my research into the Columbine High School massacre, I would have been flummoxed. But after 16 years studying these types of killers, his inconsistencies couldn't have been more consistent. Flanagan was a classic "injustice collector."

Retired FBI profiler Mary Ellen O'Toole, who is widely regarded as one of the smartest people alive on these cases, described Flanagan as such on an appearance on CNN last week. And it was an easy call—Flanagan could be the case study. O'Toole published a primer on injustice collectors in the journal Violence and Gender last year, and many of her descriptors could be lifted right out of this case: "nurses resentment ... accumulating real or imagined slights, insults or putdowns ... could not get along with his co-workers ... disproportionate and aggressive response." Collectors magnify petty "injustices" and perceive them as intentional and purposeful. Over time, he forms a worldview of himself as victimized, bullied, discriminated and disrespected.

How does this lead to murder? The angriest collectors lash out in erratic and disproportionate ways. But they almost never kill out of the blue. One of the most notorious killings of this type was the Bath, Michigan massacre in 1927. Long before the big crime, Andrew Kehoe left a searing trail of fierce retaliation for petty offenses. He killed a family friend's dog, telling her it barked too much. He beat his own horse to death for laziness. He fought with co-workers, lost his job, lost re-election and was losing his house and farm. Then he set about his revenge. He spent months wiring the school basement with hundreds of pounds of dynamite. On May 18, he murdered his wife, who had been burdening him with tuberculosis treatment, and firebombed his farm, burning two trapped horses to death. Then he detonated the school. Forty-five people died, including 38 kids. At least 58 were injured. Though widely forgotten, because it did not breed copycats, it remains the worst school massacre in American history.

After Columbine, O'Toole led a comprehensive FBI investigation of school shootings, which included an in-depth review of eighteen previous cases. She authored its 2000 report. In quite a few cases, the pattern of injustice collectors leapt out at her team. These very angry collectors responded to "injustice" with  revenge fantasies—but not the way most people think of revenge, or wield it. For most of us, revenge is highly personal, and tit-for-tat: He did this to me, I'll pay him back with that. Collectors who kill get overwhelmed by their enemies list. Everyone is on it. Chance encounters, people he doesn't even know: That bus driver who braked too abruptly three summers ago; the woman at Starbucks who coughed too much in 1983; the dirty look from the girl in high school Spanish class, sophomore year. They ruminate over petty slights, often imaginary, and spit them back in specific detail years later.

Fired Los Angeles cop Christopher Dorner reached back further. In his murder manifesto, Dorner complained about a kid who called him a racist name in first grade. He described his response as "swift and non-lethal. I struck him fast and hard with a punch and kick.” Non-lethal, in first grade. But he was not satisfied. At the age of 33, Dorner still remembered the kid's name, as well as the principal's. He recounted it all in "Last Resort," his manifesto, along with similar incidents working for the LAPD. He posted it to Facebook in 2013, to justify his killing spree targeting police officers around Los Angeles. The murders and ensuing manhunt stretched on for ten days, before police killed him in the San Bernardino Mountains. Dorner managed to kill four and injured three.

Triviality is the collector's hallmark, coupled with the absurdly disproportionate fury it inspires. As he hatches his plan, the collector ponders how to punish his hate list, which is really everyone. A year before Columbine, Eric Harris began his journal with "I hate the fucking world..."—a sentiment backed up on every page. He compiled a massive all-caps HATE list, of the petty offenses he blamed for his rage: people mispronouncing "expresso," slow drivers in the fast lane, and “[t]he WB network!!!! Oh Jesus, Mary Mother of God Almighty, I hate that channel with all my heart and soul.”

Flanagan expressed admiration for the killers at Columbine and Virginia Tech. O'Toole expects investigators to discover troves of information Flanagan gathered on previous killers and their intentions. Like Flanagan, Harris ripped on racists in the middle of diatribes against other races. Harris slammed "niggs" relentlessly, often in combinations, like "niggers and spics and chinks." He found that funny and easily justified: "sometimes they are so fucking retarded they deserve to be ripped on."

We can't be certain who Flanagan was lashing out at, but the pattern suggests it was all of us. That's why it was so irresponsible for Virginia Governor Terry McAuliffe to label him "a disgruntled employee" within hours, and for the press to describe the murders as a "workplace shooting." Flanagan was disgruntled with humanity, and while he surely enjoyed wreaking vengeance on his employer, he was clearly maximizing exposure. This was an act of theater, and Flanagan chose his stage thoughtfully. If a primary aim were punishing the managers who had wronged him—and his cats—wouldn't he have gone straight to their offices, or their homes and shot them? He passed them over for live television, and targeted a woman he'd never met, who was a darling of the audience who felt they knew her.

Injustice collectors tend to leave explanations. They demand to be heard. Before his Facebook manifesto, and two days before his rampage, Christopher Dorner sent CNN’s Anderson Cooper a DVD outlining his grievances. That same year, 2013, Jennifer Jakeman Cooper studied a small group of serial, spree, and mass killers who left would-be manifestos. Most of the texts were rambling, repetitive, and disorganized. The collectors' grievances can typically be lined up beside a corresponding paper trail documenting that he, in fact, was the problem. WDBJ management began filling Flanagan's employee file with examples in 2012. “On three separate occasions in the past month and a half you have behaved in a manner that has resulted in on [sic] or more of your co-workers feeling threatened or uncomfortable,” one memo stated. It was written by the news director just two months into Flanagan's tenure. Other memos chided him for aggressive behavior and "misinterpreting" what his co-workers did and said. He'd previously been fired from a Tallahassee station for "misbehavior " against co-workers.

In literature, we'd call collectors like this an unreliable narrator of their own story, including their suicide. "Even my cats died because of [the station]," Flanagan’s suicide letter said—a statement that even Dr. O'Toole, who has faced down countless murderers and serial killers, was taken aback by. I discussed Flanagan with her and other experts on mass killers this weekend. "That failure to take responsibility for his actions!" O'Toole said. He had a few wake-up calls, which would provoke most people to consider their own flaws: no job, slaughtered cats. "He just doesn't," she said. "In the face of so much, he just doesn't."

But injustice collectors never see fault in themselves. "They do not engage in serious self-examination to look at their own faults or shortcomings, it is always the fault of someone else, always," said Gary Noesner, who helped create and lead the FBI's hostage negotiation unit, and served as chief negotiator for ten years. "They have almost no anger management coping mechanisms. My view is that these are the most dangerous individuals that we face in society."

Flanagan's sense of faultlessness echoed his Columbine forerunner. When Harris was arrested on three felony counts for breaking into a locked van and stealing electronic equipment the year before Columbine, he blamed the owner. "How come, if I'm free, I can't deprive a stupid fucking dumbshit from his possessions if he leaves them sitting in the front seat of his fucking van out in plain sight and in the middle of fucking nowhere," Eric howled in his journal."Fucker should be shot."

Collectors tend to be egocentric and narcissistic. Unbridled superiority leaps off Flanagan's suicide notes, and his work history. A third TV station, in Alabama, chose not to hire him when the news director called his references, who described him as “exceedingly difficult to work with.” Is there a greater tell of blind superiority and reckless infallibility than listing people eager to vilify you on your own job application?

Whatever you do, don't cherry-pick quotes from a collector and believe it explains him. They tend to state their motives emphatically, but they are mostly outbursts. They're emphatic about everything. Were the Charleston murders really the "the tipping point" that Flanagan said they were? Was he trying to start a race war? Maybe. But one of the primary targets of Flanagan's anger was black men. (Also white women, but not the white men running the country.) The Columbine killers, who Flanagan cited, said they also hoped to jump-start a revolution, but did nothing to foment one. Eric Harris wasn't hunting slow drivers, expresso-speakers, or the WB network at Columbine High. And certainly not “niggers and spics and chinks” in his mostly-white school. The Bath school bomber said he was avenging a local tax increase to fund the school, which he blamed for his foreclosures and financial ruin.

Don't believe them. Injustice collectors hate everyone, and that's not what we mean by a "hate crime." That term is for perpetrators targeting a specific group or class. Collectors like Flanagan are usually lashing out at all of us. Most are targeting no one, even the unlucky victims they kill to even the score with the human race. "The goal of someone who hates another person or group is to destroy them," O'Toole said. "The hater turns people into objects. They are no longer human and easier to kill."

O'Toole made an interesting distinction between transient emotions and the endurance of hate. Anger and even rage are temporary feelings. Rage may drive you to the urge to kill, but if you come down from the brink, the feeling will pass. "Hatred is a constant emotion, which is why it is so hard to 'rehabilitate' a hater," she said. 

And it’s hard to defuse a collector once his rampage begins. "As a negotiator, this person always scared me the most," Noesner said. Their potential for a violent conclusion runs high. Noesner described a collector as a cup filled with emotions, always working up to a boil. He found them "supremely challenging to negotiate with, because no matter what you do, you have a difficult time tamping down those emotions." Hostage negotiation is all about easing people toward a place where they think clearly to make better decisions. "For [collectors], once they work up to a frenzy, there is no turning back, no moderation," Noesner said. "Anger drives every waking minute, with a strong sense of revenge and a desire to make someone pay."

As Flanagan wrote in one of his manifestos, "I've been a human powder keg for a while...just waiting to go BOOM."

Most of us have been known to bear a grudge, and we're not likely to kill. That’s why O'Toole distinguishes two types of collectors: "non-aggressive" and "dangerous." The dangerous category is distinguished by at least one incident where the person lashed out aggressively and disproportionately to the supposed injustice. Injustice collector Aaron Alexis killed twelve people at the Washington Navy Yard in 2013. Years earlier, he felt mocked by construction workers over a parking dispute. He stewed over it for weeks, and finally shot up one of the worker's vehicles.

Elliot Rodger was reported to police for trying push to push several young women off a ten-foot ledge at a college party in 2013. He began plotting an all-out attack for Halloween, chickened out, and the following May, he struck. He posted "My Twisted World" to the web—his 137-page manifesto justifying his rampage around University of California, Santa Barbara. He lambasted all sorts of groups and ultimately "humanity," but saved most of his vitriol for women, guilty most often of rejecting him. His spree included an attack on a sorority house, where he killed two women and injured another. He also stabbed three men in his apartment, shot a student at a deli, and drove around shooting pedestrians. He killed six people and injured fourteen before killing himself.

Flanagan left a litany of disproportionate responses this week, ranging from the quietly obnoxious to violent. He got so unruly when WDBJ finally fired him that they called the police and co-workers locked themselves in another office for safety.

Flanagan labeled his rants "suicide note," but treat that assertion skeptically as well. Few of this breed are yearning for death as an antidote to misery, but their homicidal lust is so strong that they're willing to sacrifice themselves to enact justice. What other option is there? Get caught, and allow the inferior authorities to pass judgment? Ha! Like the Bath and Columbine killers and many others, Flanagan killed himself to escape capture. Collectors like to have the last word.