LONDON (Reuters) – A gunman who killed 49 people at two New Zealand mosques live-streamed the attacks on Facebook for 17 minutes using an app designed for extreme sports enthusiasts, with copies still being shared on social media hours later.The live footage of Friday’s attacks, New Zealand’s worst-ever mass shooting, was first posted to Facebook and has since been shared on Twitter, Alphabet Inc’s YouTube and Facebook-owned Whatsapp and Instagram.

Facebook, Twitter and YouTube all said they had taken steps to remove copies of the videos. Facebook said it had deleted the gunman’s accounts “shortly after the livestream commenced” after being alerted by police.

But Reuters found videos of the shooting on all five platforms up to 10 hours after the attacks, which began at 1345 local time in the city of Christchurch. Twitter and Google said they were working to stop the footage being reshared. Facebook did not immediately respond to additional questions.

In a 15-minute window, Reuters found five copies of the footage on YouTube uploaded under the search term “New Zealand” and tagged with categories including “education” and “people & blogs”. In another case, the video was shared by a verified Instagram user in Indonesia with more than 1.6 million followers. The user did not respond to a Reuters request for comment.

Facebook, Twitter, Alphabet Inc and other social media companies have previously acknowledged the challenges they face policing content on their platforms.

The shootings in New Zealand show how the services they offer can be exploited by extremist groups, said Lucinda Creighton, senior advisor to the Counter Extremism Project. She said the attacks were shown live on Facebook for 17 minutes before being stopped.

“Extremists will always look for ways to utilise communications tools to spread hateful ideologies and violence,” she said. “Platforms can’t prevent that, but much more can be done by platforms to prevent such content from gaining a foothold and spreading.”

COMPUTER GAME CARNAGE

The gunman filmed and shared the attacks using a mobile phone app called LIVE4, which allows users to broadcast directly to Facebook from personal body cameras, according to the app’s developer and a Reuters review of videos available online.

The app is usually used to share videos of extreme sports and live music, but on Friday the footage recreated the carnage of a computer game, showing the attacker’s first-person view as he drove to one mosque, entered it and began shooting randomly at people inside.

Alex Zhukov, founder and chief technology officer of LIVE4 developer VideoGorillas, said the LIVE4 services transmitted footage directly to Facebook and his company did not have the ability to review it first.

“The stream is not analysed, stored or processed by LIVE4 in any way, we have no ability (even if we wanted to) to look at the live streams as they are happening or after it’s completed,” he said in written comments to Reuters.

“The responsibility for content of the stream lies completely and solely on the person who initiated the stream.”

He said the company condemned “the actions of these horrible persons and their disgusting use of our app for these purposes … We will do whatever is humanly possible for it to never happen again.”

New Zealand’s Department of Internal Affairs said people posting the video online risked breaking the law.

“The content of the video is disturbing and will be harmful for people to see,” the department said. “We are working with social media platforms, who are actively removing this content as soon as they are made aware of an instance of it being posted.”

But private online communities dedicated to violent content were still looking for ways to share copies of the video.

Members of a group called “watchpeopledie” on internet discussion board Reddit, for example, discussed how to share the footage even as the website took steps to limit its spread.

Reddit – which has over 20 investors, including Conde Nast owner Advance Publications – said it was actively monitoring the situation in New Zealand.

“Any content containing links to the video stream are being removed in accordance with our site-wide policy,” it said.

One Reddit user said in a post they had sent a video of the attack to more than 600 people before having their account temporarily suspended for sharing violent content.