SEATTLE >> The attacker who killed two people in a shooting at a German synagogue live-streamed the assault on Twitch, a video service owned by Amazon. It was one of the first violent attacks streamed on the service, which is best known for letting people watch others play competitive video games.

Here’s what you need to know about Twitch.

WATCHING PEOPLE PLAY

Twitch is a site where people can livestream video games as they’re playing, usually providing tips and commentary while others watch. The platform has boomed in popularity over the last few years, and played a key role in boosting the spread of “esports,” or competitive video gaming.

Popular Twitch gamers can have millions of followers. The platform itself has more than 100 million monthly users.

NON-VIDEO GAME VIOLENCE

The German shooting may have been the first real-world violent attack livestreamed on Twitch. The company said it found and took down the video with “urgency” and said it was “shocked and saddened by the tragedy.” But the video, which has since spread to other corners of the internet, is reportedly 36 minutes long.

Twitch said only about five people saw the livestream, but 2,200 viewed the finished recording of the video for the next 30 minutes until Twitch took it down.

Twitch has faced other complaints in the past — largely from female gamers who say they have been harassed on the site, echoing an undercurrent of sexism that has long been an issue in gaming culture. It has policies in place against hateful conduct and harassment and asks users and streamers to report inappropriate conduct.

The attack in Germany echoed a March assault in Christchurch, New Zealand. Then, the perpetrator live-streamed his attack on Facebook. The social network subsequently said it was working on restricting some users with previous rules violations from using Facebook Live. It also continues to work on artificial intelligence technology that can detect violent videos to prevent them from being re-shared.

It’s hard to guess why Twitch was chosen this time, said Hannah Bloch-Wehba, a law professor at Drexel University. She noted it is possible that Twitter and Facebook’s attempt to crack down on such material may be discouraging people from trying to stream violence there.

Internet companies have pledged after each attack to work on preventing such livestreams from happening again, including by advancing artificial intelligence to catch such videos. Bloch-Wehba is skeptical that those efforts alone will entirely halt the problem.

There’s an argument that the big companies should be doing a lot more, said Justin Brookman, the director of consumer privacy and technology policy for Consumer Reports.

“Companies definitely need better legal incentives to police their platforms from abuse,” he said.

Twitch said it found evidence the video was shared in messaging services outside the platform. It shared a copy, or “hash,” of the video with other tech companies so they could try to halt the spread of copies on their own sites.

HOW TWITCH GREW

Seattle tech giant Amazon bought Twitch for $970 million in 2014. It had already attracted a critical mass of video-game streamers, and remains the default place to watch gamers play.

It also has drawn competitors such as Microsoft-owned Mixer and Google-owned YouTube, which have angled for a slice of that business. Mixer even poached one of Twitch’s star gamers , a Fortnite player known as Ninja, in August.