https://arstechnica.com/tech-policy/2019/03/social-media-sites-struggle-to-contain-video-of-new-zealand-shooting/

A white nationalist who murdered an estimated 49 Muslims in Christchurch, New Zealand, on Friday livestreamed a portion of his gruesome crime on Facebook, sending social media companies scrambling to contain the spread of the video.

Major social media platforms, including Facebook, YouTube, and Twitter, have terms of service prohibiting graphically violent videos. Officials worry that wide distribution of such videos boosts the profile of mass shooters and could inspire copycats. It can also be painful for victims' families.