The gunman who killed 11 congregants at a Pittsburgh synagogue last Saturday could herald a new era of hate crimes, according to an expert who has tracked similar attacks since the 1990s.

“We have more people drawn to white supremacist rhetoric who see themselves as on a mission to change the world,” said criminologist Jack McDevitt, the director of the Northeastern University Institute for Race and Justice. “That’s going to change the character of hate crimes in America.”

The Pittsburgh shooter’s online activity distinguished him from the majority of people who commit hate crimes. He was a deeply committed white supremacist who steeped himself in anti-Semitic and xenophobic propaganda. He attacked the Tree of Life synagogue with a clear purpose: It was not only a Jewish house of worship, but was also associated with activists who worked to welcome refugees in America.

McDevitt said that, historically, the most typical bias crime is an impulsive act of intimidation. “Since at least the 1990s, hate crimes have mostly been committed by groups of teens or young men who want a thrill,” he said. “So they decide to go out on a Friday night and find a gay person, a black person, or some other minority to beat up.” If these kinds of attacks involve weapons, the perpetrators typically use what McDevitt calls “situationally available” weapons like bricks, rocks, or glass bottles.

The Pittsburgh shooting was different because it was a premeditated act that served a larger political purpose of punishing Jews who help refugees. McDevitt said these kinds of attacks, perpetrated by people he calls “mission offenders,” are both comparatively rare and more likely to involve guns. Deliberately choosing a target like a synagogue and assembling an arsenal implies a rare degree of ideologically committed racism and planning. Very few people will be motivated to carry out such an attack, but those who do will want to inflict the most damage, so they will use the most lethal weapon they can get. That’s usually a gun.

Data on hate crimes is notoriously inconsistent, but it suggests that the Pittsburgh shooter was part of a small subset of attackers. The Trace reported that from 2011 to 2013, the Federal Bureau of Investigation received 8,132 reports of hate crimes from local law enforcement agencies that participate in the bureau’s Uniform Crime Report. Of those, only 207 involved a gun. But according to the Bureau of Justice Statistics’ National Crime Victimization Survey, based not on police reports but self reports from the public, Americans are subject to more than 200,000 hate crimes every year. An analysis of the BJS data by the Center for American Progress, a Democratic Party-aligned policy think tank, estimated there were 46,500 hate crimes involving guns between 2010 and 2015.

Newly updated figures from the Anti-Defamation League, a Jewish anti-bigotry organization, show that the frequency of far-right violence varies by year, with no clear trend line. The number of attempted and successful right-wing terror attacks peaked at 13 in 2015, the year of the Charleston church shooting, and then fell to six in 2016. Last year saw 12 attempted and successful terrorist killings by members of the far right, the second highest annual total. So far this year, the ADL has counted only four such attacks, including the Pittsburgh synagogue shooting.

A separate report by the group released last June showed that slightly more than half of all attacks by members of the extreme right between 1993 and early 2017 that resulted in injuries or death were committed with firearms.

The Pittsburgh shooting eclipsed the Charleston church shooting to become the deadliest ever shooting committed by a member of the extreme right, and ranks as the second-deadliest right wing terror attack of any kind after the Oklahoma City bombing in 1995.

For much of the 1990s and the early 21st century, hate groups had a hard time radicalizing people to the point that they would take up arms. Federal authorities and activist organizations like the Southern Poverty Law Center used the courts to dismantle groups that tried to grow the white supremacist movement, radicalize people, and foment violent hate crimes.

In 1981, the SPLC successfully sued a Texas-based paramilitary Klan group that harassed Vietnamese fishermen who had resettled in Galveston Bay. They had threatened the refugees, destroyed their property, and used guns to intimidate. A court seized the Klan’s training camp and issued an injunction against its members.

In 1990, the SPLC won another court case against a hate group, arguing that leaders of a group called the White Aryan Resistance were responsible for inspiring skinheads who murdered an Ethiopian student in Portland, Oregon. Jurors imposed a $12 million penalty on the leaders of the hate group.

The white power movement adapted to lawsuits like these, developing a strategy known as “leaderless resistance.” Organizations and prominent racists would keep a lower profile, and at least in word disavow violent hate crime — but hoped to inspire lone actors, as in the case of Oklahoma City bomber, Timothy McVeigh. The tactic made it difficult for activists and law enforcement authorities to tie hate groups to hate crimes. But it also was a diffuse and unreliable model of organizing, considering the difficulties of reaching potential recruits or sympathizers in the pre-Internet age.

A lot has changed since the 1990s. Decades ago, white power literature and propaganda circulated through underground networks, limiting its reach. Today, marginalized racists like the Pittsburgh shooter can connect with one another through platforms like Gab, a social network favored by the alt-right, to circulate white power propaganda, radicalize one another, and broadcast violent threats. Gab was forced to shutter after the Pittsburgh shooting when its web-hosting company cut ties with it.

“The messaging empowers people to act on their own,” said McDevitt. As racists spread hate speech online with greater ease and political leaders like President Donald Trump demonize the same groups targeted by white nationalists, McDevitt said, “I fear we will see more of these kinds of shootings.”