Flowers and balloons are accumulating outside the studio of WDBJ7 in Roanoke, Va., one day after an angry former reporter shot and killed two people during a live broadcast. (AP)

On Sunday, criminal justice professor Adam Lankford stood in front of a crowd of sociologists to explain how American culture contributes to the all-too-frequent American mass shootings. It’s not just that we have a lot of guns, he said — though he does believe that the high rates of firearm ownership are partially to blame. It’s the social strains of American life — the false promise of the American dream, which guarantees a level of success that can’t always be achieved through hard work and sheer willpower; the devotion to individualism and the desire for fame or notoriety.

Millions of Americans feel these strains and never commit a crime. But for a small handful, they breed the kind of resentment and fury that can explode into violence.

When an embittered former Roanoke reporter opened fire on his onetime colleagues three days later, interrupting their live broadcast to ensure that his attack made it on TV, it was as though he was trying to prove Lankford’s point.

[Two Roanoke journalists killed on live television by angry former colleague]

The shooter, 41-year-old Vester L. Flanagan II, embodied every problem Lankford had identified in his global review of public mass shootings since 1966. He was reported to be frustrated with his patchy career as a television news reporter. He aspired to fame — either behind an anchor desk, or, according to photos shared on his Twitter account, through acting and modeling — and he got it, in a way, via the TV and GoPro footage of the slayings.

Authorities have identified Vester Lee Flanagan as the suspect in the shootings deaths of journalists Alison Parker and Adam Ward during a live TV broadcast near Roanoke, Va. (Jorge Ribas/The Washington Post)

Flanagan admired other mass shooters whose names have become inextricably linked to those of the schools where they committed crimes. And although he was the one who allegedly raised a gun and pulled the trigger, ending two lives, he saw himself as a victim.

“WDBJ7 made me snap . . . they sure did. They are responsible for all of this!!!” reads a memo attributed to Flanagan in which he raged at former coworkers who he said harassed him for his race and sexuality (Flanagan was black and gay) and decried the killing of nine parishioners at a black church in Charleston, S.C., earlier this year.

At three deaths, Flanagan’s alleged attack does not qualify as mass killing — in the macabre hierarchy of violent crimes, a shooter must take four lives to be granted that title (this is according to Lankford’s definition — definitions vary). But according to Lankford’s analysis, he was the archetype of the American public mass shooter, someone who sought fame and a kind of meaning through death when he could not find it in his own life.

Lankford, a criminal justice professor at the University of Alabama, is the author of a new study on what he calls the “exceptionally American problem” of public mass shootings. The study was presented at the annual meeting of the American Sociological Association this week and will be published in peer reviewed journals later this year.

The United States, according to Lankford’s analysis, is home to just 5 percent of the world’s people but 31 percent of its public mass shooters. Even more stunning, between 1966 and 2012, 62 percent of all school and workplace shooters were American. At 90 mass shooters in less than 50 years, the U.S. has five times as many as the next highest country on the list (the Phillippines).

[Father of slain TV reporter Alison Parker: ‘My grief is unbearable.’]

One explanation is Americans’ high rate of firearm ownership. All five of the countries with the largest number of guns per capita (of which the U.S. is No. 1) ranked among the top 15 countries for public mass shootings, including two countries with reputations for safety, Switzerland and Finland. Many other studies have found a correlation between local gun ownership rates and deaths from shootings.

But that’s not enough to explain why mass shootings happen so much more often here than anywhere else. There are also cultural factors at work, Lankford argues. The things that Americans believe make us exceptional — our emphasis on individualism, our sense of destiny, our wealth-and-fame-based standards for success — also contribute.

[Cameraman Adam Ward, 27, was planning to get married before he was killed outside Roanoke]

The connection begins with something called “strain theory,” developed by sociologist Richard Merton in the 1930s. According to the theory, Lankford says, “deviance occurs because individuals who strive to meet culturally defined goals lack the means to do so.”

This is especially salient in the U.S., where the “American Dream” promises a better life than one’s parents for anyone who is willing to work for it. According to a 2010 survey, 81 percent of American high school students believe they will have a “great paying job” by age 25. A similar survey conducted in 2014 found that 26 percent of high schoolers expected that they would soon be famous. Nearly one third of college freshman expect to eventually get an M.D. or PhD (though only about 5 percent do).

“There’s a sense in which these aspirations are subject to that axiom that the bigger they are the harder they fall,” Lankford said. “If you’re reaching for the stars and you come up short, that’s perhaps more frustrating and devastating.”

[In alleged shooter’s memo, rage at co-workers and Charleston shooter]

The reality is that very few people achieve the wealth, fame and prestige we’re all socialized to believe is our destiny. When the socially sanctioned path toward success doesn’t take people where they want to go, some resort to other means. Negative social interactions — lack of friends and mentors, failures in school — and mental illness can exacerbate the problem, making them believe that “their dreams are hopeless,” Lankford said.

The strain theory framework has traditionally been used to explain high rates of crime, particularly in poor and marginalized communities, but Lankford says it’s particularly apt to describe mass killings. Unlike most other offenders, shooters are likely to leave behind memos or manifestos purporting to explain their actions. And most of them, including Flanagan, cite negative social interactions and blocked goals as their primary motives.

“They are in real pain, but they’re eager to blame that pain on those around them,” Lankford said.

Workplaces and schools — or, in Flanagan’s case, former colleagues — are the symbolic sources of their strain; by attacking them, shooters seek to exact revenge on the people and institutions they believe have kept them down. In the U.S., the strain of unmet expectations and unrealized goals is more pressing than perhaps anywhere else, so it makes a gruesome kind of sense that this country is home to nearly two thirds of the world’s school and workplace shooters.

The brazen violence of mass shootings sates another particularly American craving: the desire for fame at any cost.

“The priority of fame is more common and stronger in the U.S. than perhaps in any other culture in the world,” Lankford said. And at the same time, “the distinction between fame and infamy seems to be disappearing.”

We are the country that gave rise to reality television and the phrase “I’m not here to make friends,” Lankford points out. We already reward people for being arrogant, aggressive and vitriolic with book deals and contracts for their own clothing lines and incessant news coverage. It’s arguably easier to become infamous in the United States than it is to win fame. Yes, your name with forever be tinged with tones of scorn, but “all publicity is good publicity,” right?

“It’s probably not surprising that, for a small percentage of people, they’ll take the next step of guaranteeing themselves fame by killing,” Lankford concluded, soberly. “… They fantasize about going out in a blaze of glory.”

It’s not difficult to imagine that Flanagan, as Lankford put it, entertained these kinds of “delusions of grandeur.” He sought to become a television news anchor — a public, high profile and prestigious position. In the memo sent to ABC News, he described himself as a victim of a conspiracy of racist and homophobic harassment, using phrases like “out to get me.”

Ultimately, the Charleston massacre — a horrific attack on a black community — convinced him that his aspirations were in fact hopeless. There was nothing else to do but take his life, and those of 24-year-old Alison Parker, a bright reporter and beloved daughter, and 27-year-old Adam Ward, a camera man with a fiancee and an easy laugh.

“[I] tried to pull myself up by the bootstraps,” Flanagan wrote in his memo, according to ABC, but, “The damage was already done and when someone gets to this point, there is nothing that can be said or done to change their sadness to happiness.”