It's an unfortunate sign of the times we live in that this has to even be mentioned, but here's a list of some of the false stories circulating.  There are several hoaxes going around about the perpetrator's identity as well as about supposed victims who weren't actually there, the right-wing claim that the shooter was involved with Antifa has no basis in known fact, and the Facebook page purported to have belonged to him that lefties have been sharing all over social media is fake.  Don't spread this stuff, and come down hard on anyone you know who does.

https://www.buzzfeed.com/talalansari/fake-news-about-the-texas-church-shooting?utm_term=.ewym7nlQR#.vowGxWbJ8