It seems like every week a new terrible crime is streamed on Facebook Live, and this week was unfortunately no exception. This latest case involved the gang-rape of a 15-year-old girl on Facebook Live that was witnessed by dozens of people — and reported by no one. This is obviously extremely troubling, but it does raise a good question: what should you do if you see a crime committed on the video streaming tool?

According to Chicago police, it’s important to first call 911. Even if you can’t tell where the video is being shot, authorities say it’s vitally important for law enforcement to be made aware of the video. Second, record the video with your phone. The person creating a live stream can end it at any time, so it’s important to keep the video as evidence if necessary. Lastly, report the video and do not share it no matter what. Sharing the video only increases its spread, and is capable of hurting the subject of the video even more.

Reporting criminal videos to Facebook enables the site to become aware of the situation faster, work with law enforcement and, perhaps most importantly, remove the video. If any one of the approximately 40 people watching the video had reported it, the site could have acted sooner to stop it.

Facebook catches a lot of flak for not doing enough to automatically find and remove disturbing videos, but it’s still important for users to do their part to keep this kind of content off the site.