Twitch, the Amazon-owned live-streaming platform known for its video game content, is developing another, darker reputation as a place to find footage of mass shootings.
On Wednesday, a heavily armed man with a head-mounted camera live-streamed his shooting rampage in Halle, Germany, on Twitch for more than 35 minutes. Two people were killed and two others injured in the attack, which took place outside a synagogue and in a kebab shop.
Twitch said on Twitter that only five people had watched the live stream of the shooting. But 2,200 people viewed a recording of the attack, which stayed up for 30 minutes before it was flagged and removed.
Last year, a Twitch live stream from a gaming tournament in Jacksonville, Fla., captured part of a shooting in which three people, including the gunman, died. In June, Twitch sued users who had posted footage of an attack in March involving mosques in Christchurch, New Zealand.
On Wednesday, the company said in a statement that it was “shocked and saddened” by the shooting in Germany.
“Twitch has a zero-tolerance policy against hateful conduct, and any act of violence is taken extremely seriously,” Brielle Villablanca, a spokeswoman for Twitch, said in the statement. “We worked with urgency to remove this content and will permanently suspend any accounts found to be posting or reposting content of this abhorrent act.”
But footage and clips of the attack began to proliferate quickly on other platforms, including Twitter and the video publishing site Streamable. Versions of the video reached more than 15,000 accounts on the messaging platform Telegram within half an hour, according to an analysis by Megan Squire, a computer science professor at Elon University in North Carolina.
Ms. Squire, who studies online extremism, said she monitored dozens of “very severely racist, violent channels” that promote white supremacy. On several channels, users debated whether the gunman should be made into a saint, according to screenshots she shared.
“Telegram exists as a forwarding network — that’s the main way the information flows,” she said. “It’s a very efficient mechanism for them.”
The Global Internet Forum to Counter Terrorism, a nonprofit organization formed in 2017 by Facebook, Microsoft, Twitter and YouTube, said in a statement that it was “actively removing perpetrator-created content related to the attack” in an attempt “to prevent its viral spread across our services.” Amazon is also a member of the forum.
The footage that appeared on Twitch was posted from an account created two months ago.
The assailant identified himself in accented English as “Anon” before denying the Holocaust, complaining about feminism and immigration and saying that “the root of all these problems is the Jew.”
He then drove to a synagogue on Halle’s Humboldt Street, an arsenal of weapons visible in his car. He struggled to enter the synagogue. After a woman spoke to him as she passed in the street, he shot her in the back, and then shot her several more times after she collapsed.
Unable to enter the synagogue even after shooting at the door, he drove to a kebab shop. He fired at two men cowering behind a beverage machine and then went outside, where he fired at several pedestrians. Later, he re-entered the shop and shot the body of one victim several times.
Twitch has doubled the number of moderators it employs this year, though it would not specify how many.
The company has been trying to broaden its appeal beyond video games, courting advertisers and soliciting content from artists, musicians, chefs and others.
Emmett Shear, the chief executive of Twitch, said at the company’s Twitchcon event in San Diego last month that safety was “a big concern,” acknowledging that users had been disappointed in the platform’s moderation practices after encountering “a lot of issues.”
“We haven’t always been consistent in our enforcement,” he said. “You have to remember we have to do this 24/7, in many different languages, in many different countries and time zones.”
He said improving Twitch’s moderation process, clarifying its community guidelines and providing more transparency would be “a perpetual investment for us.”
“It’s one of the biggest challenges facing every social media service on the internet, and particularly facing Twitch,” he said.