The shooter wore a head-mounted camera to livestream the attack, and in his social posts and manifesto suggested that he wanted to stoke tensions that supported his anti-immigrant agenda. There's been a concern that spreading the video is giving the attacker the exposure he wanted in addition to traumatizing viewers.

While the removal rate suggests that Facebook is having some success pulling the video, it also shows how difficult it can be to contain the spread of material like this. About 300,000 copies made it to the site before they were taken down, after all. The company's existing mix of automated and human moderation can only do so much when it's relatively easy to upload a video or make edits that can bypass content filters. Facebook and other internet firms may end up reviewing their methods to see if they can speed up video removals and make it harder to spread footage like this in the first place.