The man who allegedly opened fire in a Pittsburgh synagogue Saturday morning, killing 11 people and injuring six, was reportedly a frequent poster on Gab, a relatively new social network that has attracted many from the far-right fringe.

Robert Bowers, the suspected shooter, reportedly joined Gab at the beginning of this year, using it to post a series of anti-Semitic messages and redistribute many more from other users. Immediately before he allegedly attacked the synagogue, Bowers took aim at HIAS, a Jewish organization that helps refugees.

"HIAS likes to bring invaders in that kill our people," he wrote, according to an archive of his Gab posts. "I can't sit by and watch my people get slaughtered. Screw your optics, I'm going in.

Read more: Here's what we know about Robert Bowers

Gab, which bills itself as the free-speech alternative to Facebook and Twitter, has become a haven for far-right extremists. The site does not police hate speech, instead encouraging users to take advantage of its tools to filter out posts they find offensive.

Here's what we know about Gab: