As a sociologist at Harvard Kennedy School’s Shorenstein Center, I study how technology is used by social movements, including groups on the far left and the far right. Since the uprisings in the Middle East and elsewhere in 2011, we have witnessed thousands of protests and events inspired by and organized through social media. Progressive social movements routinely use networking technologies to grow their ranks and publicize their ideas. White supremacists have their own ways of deploying the same technology.

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In the aftermath of outbursts of violence such as the one in New Zealand, traditional news outlets draw heavily on social-media postings for insights into the perpetrator’s motives and mine them for details that make stories sound more authoritative and vivid. Certain oddball phrases, internet memes, and obscure message boards garner mainstream attention for the first time. Inevitably, people Google them.

The extra attention that these ideas gain in the aftermath of a violent attack isn’t just an unfortunate side effect of news coverage. It’s the sound system by which extremist movements transmit their ideas to a broader public, and they are using it with more and more skill.

One variable remains consistent across all networked movements: The moderation policies of different platforms directly affect how groups amplify political ideologies online. White supremacists and other extremists tend to use anonymous message boards to plan manipulation campaigns. These places traffic in racist, sexist, and transphobic content and link to obscure podcasts and blogs. Moderation is rare and tends to occur only when too much attention is drawn to a certain post. In some forums, posts self-delete and leave few traces behind.

Far more useful in reaching a new audience are places such as Twitter, YouTube, and Facebook, which remove objectionable content—but may not do so before it spreads virally.

Taking advantage of that dynamic, the murderer in New Zealand posted a full press kit on an anonymous message board prior to live-streaming his terrifying acts on Facebook. Many have labeled it a manifesto, but it reads more like a collection of copy-and-pasted white-supremacist conspiracy theories and memes. It would never have been notable on its own. This individual did not have the power or influence to boost these worn-out tropes. This manifesto could probably have existed in perpetuity on obscure document-hosting sites, and no one would have noticed. For platforms, this kind of content is simply white noise.

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Explosive violence was the signal necessary to call attention to these posts. The New Zealand attacker used the live-streaming feature of Facebook to control the narrative, even to the point of saying “Subscribe to PewDiePie”—a meme referencing a popular right-wing YouTube influencer—during his broadcast. He succeeded in linking his deeds to PewDiePie’s fame. As of today, Google-search returns on “PewDiePie” include references to the Christchurch attack.