“Now in this world, there’s no gatekeeper,” he said.

Facebook moderators take videos down if they glorify violence, but allows them to remain if they appear to be trying to raise awareness. In some cases, as in the video of Mr. Perkins, Facebook adds a disclaimer: “Warning — Graphic Video. Videos that contain graphic content can shock, offend and upset. Are you sure you want to see this?”

Whether for advocacy or for mere voyeurism, the video of Mr. Perkins has been shared thousands of times on social media. Though relatively infrequent, the list of gruesome violence accidentally captured through live streaming is growing.

• In March, a video appeared to show a Chicago man capturing his own shooting on Facebook Live. His selfie-mode video was interrupted by the sound of gunshots, the camera appeared to fall to the ground, and a gunman appeared to step over the camera and fire more shots.

The Chicago police said they suspected the video was linked to a shooting in the South Side, but have not confirmed it. The city has been besieged by gun violence, as documented by New York Times journalists over Memorial Day weekend.

• An Ohio teenager, Marina Lonina, 18, was accused in April of streaming a video of her friend’s rape on Periscope. She pleaded not guilty to a litany of charges as severe as the rape suspect’s. Ms. Lonina told the police that she had filmed the encounter to gather evidence.

“She was swept up by the gravity of the situation,” her lawyer, Sam Shamansky, said in April. “And as she immediately told the police, she was filming in order to preserve, not to embarrass or to shame or to titillate anybody.”