"The New Zealand police warned us about a video on Facebook shortly after the live stream started and we quickly removed both the Facebook and Instagram accounts of the shooter and the video," said policy chief Mia Garlick of Facebook for Australia and New Zealand.
A few hours after the attack, however, copies of the gruesome video continued to appear on Facebook, YouTube and Twitter, raising new questions about companies' ability to handle malicious content on their platforms.
Facebook is "removing any praise or support for the crime and the shooter or shooters as soon as we know about it," Garlick said.
The New Zealand police asked social media users to stop sharing the alleged video footage and stated that they were trying to make it take apart.
CNN is choosing not to publish more information on the video until more details are available.
Technology companies do not see this as a priority & # 39;
Friday's video rekindles questions about how social media platforms handle offensive content: are companies doing enough to try to capture this kind of content? How fast should they be removed?
"While Google, YouTube, Facebook and Twitter all say that they are collaborating and acting in the citizens' interest to remove these contents, in reality they are not because they are allowing these videos to reappear at any moment," said Lucinda Creighton , senior consultant of the Counter Extremism Project, an international political organization.
Apparently Facebook's artificial intelligence tools and human moderators appeared unable to detect the livestream of the shooting. The company says she was alerted by the New Zealand police.
"Technology companies basically don't see this as a priority, they twist their hands, they say it's terrible," Creighton said. "But what they are not doing is preventing this from reappearing."
Anti-terrorism expert John Battersby at Massey University in New Zealand, said the country was spared from mass terrorist attacks, partly due to its isolation. Social media has changed it.
"This guy broadcast live footage and his supporters cheered him up, and most of them are not in New Zealand," he said. "Unfortunately, once it's out there and it's downloaded, it can still be (online)," he added.
The release of the video could inspire the copycats, said CNN analyst Steve Moore, a retired special security agent for the FBI.
"What I would like to say to the public is this: do you want to help terrorists? Because if you do, sharing this video is exactly how you do it," Moore said.
"Don't share the video or be part of it," he added.
Hadas Gold, Donie O & Sullivan, Samuel Burke and Paul Murphy contributed to this report.