“Some people would talk about the way they enjoyed them, and how their enjoyment reduced over time,” she said. “But the things they were saying they enjoyed were symptoms of post-traumatic stress.” They were describing anxiety. They were reexperiencing their time on the site, as one might after a trauma, but describing this with a sense of accomplishment. Further, Dr. Tait said, “I noticed a desire to transmit that trauma to other people, so that you could have other people to talk about it with.”

This called to mind recent conversations she’d had with fellow Christchurch residents, one of whom had told her in a brief encounter at the supermarket that he’d watched the shooter’s video twice. He spoke abstractly about how it hadn’t affected him as much as he had expected. “It reminded me of people on Ogrish,” Dr. Tait said. “It felt to me that this guy who was watching it was a bit disappointed.”

Experts almost universally advise against casting the consumption of violent footage as a fringe phenomenon. Jennifer Malkowski, an assistant professor of film and media studies at Smith College, who uses they/them pronouns and is the author of “Dying in Full Detail: Mortality and Digital Documentary,” pointed out that Liveleak, which is just one of many sources for such footage, is ranked by the web tracking firm Alexa as the 695th biggest site in the world, right alongside The Onion, Jezebel, and Forever21. Mainstream internet platforms have thrown vast amounts of money and labor (much of it invisible) at removing nightmarish content, hiring thousands of content moderators to identify and remove often traumatic and illegal content. But “they’re circulated by many many people,” they said. “I think when you see those numbers from Facebook, you’re confronted with that reality.”

“You realize that these videos aren’t circulated by a few maladjusted individuals,” they added.

“To be focusing on the tech platforms is kind of like an imported crisis,” said Barbie Zelizer, a professor at the University of Pennsylvania and author of “About To Die: How News Images Move the Public.” She said: “You cant extricate one part of the media environment from the rest.” Conversations and norms around representing death, violence and terrorism in media span generations and mediums. (She notes in her book that Google experienced an extended surge of search for footage of a 2004 beheading of an American in Iraq.) Norms about what should be shown on television and in newspapers — which Dr. Zelizer says have become more conservative — have given way to debates about tech platforms. “There’s no question that images have impact,” she said. “But we don’t know what that impact is, not in a way that could propel some sort of reasoned set of responses.”

The big tech platforms, in other words, are inheriting, with much else, a problem that was once understood as the media’s. But services like Facebook are far larger than any individual newspaper. Big social media platforms have inherited much of the rest of the web and it’s users — including the ones who might have spent time on a site like Ogrish.

Violence and More, Made for Sharing

There are still plenty of videos of viscerally awful things on Liveleak. There are also a lot of videos about immigration, about how the media is attacking Donald Trump, about “political correctness” and about Islam. It’s one of the few platforms that still hosts videos from Infowars, which was banned from YouTube and Facebook last year, although they do not appear to garner many views.