Inspired by sermons, lectures and literature they find online, many extremists in the last decade of the digital age have been radicalized through social media. Although the internet has long been a habitat for extremism, the ease and freedom with which social media allows ideas to spread and individuals to connect has some wondering whether it is time to take more seriously the role of online networking in terrorist attacks, like last month’s shootings in New Zealand and this past weekend’s shootings in San Diego.

“The main culprits are social media and the total collapse of any sense of bipartisanship about how to fight hate in America,” Rabbi Abraham Cooper, director of global social action at the Simon Wiesenthal Center told the Washington Post in reaction to Saturday’s shooting in San Diego. “Evildoers around the world learned from the 9/11 terrorists that you don’t need the backing of a state or a mass movement. And then individuals who are probably psychiatric cases are inspired to do these things because social media spreads a culture of hate in the most public ways, and encrypted communications allows them to go private to discuss the how-tos.”

With billions of people using social media every day, it’s become a hotspot for radical activity. Notable voices within the “alt-right” community, who are frequently critiqued for having white nationalist sympathies, rose to prominence on Twitter, while the terrorist group ISIS managed to recruit large amounts of foreign agents by disseminating literature over Facebook and YouTube.

Gabriel Weimann, a professor of communications at Haifa University who has studied terrorists’ use of the internet since the 1990s, says social media doesn’t just allow terrorist to send out propaganda more easily, but also makes it easier for recruits to contact an organization.

“[Social] networking allows terrorists to reach out to their target audiences and virtually ‘knock on their doors’—in contrast to older models of websites in which terrorists had to wait for visitors to come to them,” Weimann wrote in a 2014 paper. “With social media, information consumers also act as communicators, vastly expanding the number of information transmitters in the communication market. This two-way communication promotes creation of small, diffused sets of communicators and groups.”

Charlie Sennott, a WGBH News Analyst and CEO of the GroundTruth Project, is also worried about the role social media plays in proliferating extremism. Sennott, who has covered religious extremism in the Middle East, said that while the last few tragedies have all been slightly different, they have all been connected by heavy social media usage on the part of the perpetrator.

“As someone who’s covered a lot of religious extremism in the world ... I think they do have a lot in common,” Sennott said during an interview Monday with Boston Public Radio. “There’s the obvious, that all of them are woven together with the DNA of hatred ... but there’s other things they share that are really important to think about, and that’s this idea that they’re all bound together by social media.”

Sennott is also frustrated with what he sees as a lack of attention paid to the role social media plays in diffusing radical ideas. During Monday’s interview, he pointed to the European Union’s heavier regulation of hate speech on social media as a model the United States should emulate, but lamented that little is likely to be done so long as President Donald Trump, a frequent and controversial user of Twitter, is in office.

“What’s missing from this equation? Where is the United States of America in a leadership position on the idea of how technology [spreads terrorism]?” Sennott said. “I truly try to say this in a [non-partisan] way, but c’mon, we need leadership from the White House on these big issues.”