Tim Pool read a couple of reports that said the shooter was discharged from the Army in 2008 due to mental health "concerns," and that he had no prior police record, no social media posts that could have been flagged, and no real friends to speak of.
So, universal background checks would have turned up nothing negative other than the discharge, and red flag laws would have been useless as he had no one close to him to report his behavior -- assuming he had exhibited anything troubling.
He was trained in the Army, let go for mental health reasons, committed no crimes prior to the shooting, and would have likely avoided any red flags.
2008 was 15 years ago. Was he being treated for his mental health issues? Was he on medication? Did he stop taking it? Did anyone in the mental health profession bother to check on him since he had a history? Did the Army just kick him out without offering any sort of treatment first? Seems like he'd qualify for VA benefits with a health problem diagnosed while on active duty, especially if that was the grounds for separation.
Those are much better questions that need answers than "what kind of guns" and "where did he get them?"