Shooter appears to be a white male, aged 20s or early 30s by the look of it. The t-shirt he was wearing is allegedly marked with branding for a firearms-related YouTube channel.
Edit: Possible suspects are either Maxwell Yearick, previously arrested while demonstrating against Trump in Pittsburgh on a previous occasion, or a Thomas Matthew Crooks, according to the NY Post.
Hasn’t been officially ID’d yet though, so still speculation.