There maybe more than one gunman as well and they are still at large.
There will never be another gunman in this case, even if ballistics prove a second rifle was used, and of a different caliber, and all of the witnesses swear to it, and the security cameras show more than one shooter.
The narrative is that he was a lone nut with easy access to guns and 'slime-ism had nothing to do with it. Truth be damned. The feels will tell the witnesses that they didn't see what they saw and that will be the end of it.