Read: Why conspiracy videos go viral on YouTube

Social-media companies scrambled to take action as the news—and the video—of the attack spread. Facebook finally managed to pull down Tarrant’s profiles and the video, but only after New Zealand police brought the live-stream to the company’s attention. Twitter also suspended Tarrant’s account, where he had posted links to the manifesto from several file-sharing sites.

The chaotic aftermath mostly took place while many North Americans slept unaware, waking up to the news and its associated confusion. By morning on the East Coast, news outlets had already weighed in on whether technology companies might be partly to blame for catastrophes such as the New Zealand massacre because they have failed to catch offensive content before it spreads. But the internet was designed to resist the efforts of any central authority to control its content—even when a few large, wealthy companies control the channels by which most users access information.

“Tech companies basically don’t see this as a priority,” the counter-extremism policy adviser Lucinda Creighton told CNN. “They say this is terrible, but what they’re not doing is preventing this from reappearing.” Others affirmed the importance of quelling the spread of the manifesto, video, and related materials, for fear of producing copycats, or of at least furthering radicalization among those who would be receptive to the message. “Do not share the video or you are part of this,” said a retired FBI agent who now works as an analyst for CNN.

That might be impossible. When I started catching up on the shooting this morning, I stumbled upon the video of the massacre searching for news. I didn’t intend to watch it, but it autoplayed in my Twitter search results, and I couldn’t look away until it was too late. I wish I’d never seen it, but I didn’t even get a chance to ponder that choice before Twitter forced it upon me. The internet is a Pandora’s box that never had a lid.

The circulation of ideas might have motivated the shooter as much as, or even more than, ethnic violence. As Charlie Warzel wrote at The New York Times, the New Zealand massacre seems to have been made to go viral. Tarrant teased his intentions and preparations on 8chan. When the time came to carry out the act, he provided a trove of resources for his anonymous brethren, scattered to the winds of mirror sites and repositories. Once the live-stream started, one 8chan user posted “capped for posterity” on Tarrant’s thread, meaning that he had downloaded the stream’s video for archival and, presumably, future upload to other services, such as Reddit or 4chan, where other like-minded trolls or radicals would ensure the images spread even further. As Warzel put it, “Platforms like Facebook, Twitter, and YouTube … were no match for the speed of their users.”