<< This seems way too calculated to be the result of a lovers’ quarrel >>
If the girlfriend info is correct, then I’ll bet we’ll find that at the 7:15 shooting, the guy was NOT armed at that time with two weapons, a vest with multiple clips, lock and chains, etc. He got into an argument with his girlfriend, had a pistol on him and then shot her and the RA.
Then he left, and was not thereafter identified or stopped by anyone. He went back to his apartment. Having committed a double murder, the loser figured that if he was going down for a capital crime he would take a lot of other people with him, and that’s when he loaded up with weapons and ammo and chains and went back on campus two hours later and shot many people.
The authorities should have locked down the campus until the perpetrator of the first incident was in custody or they knew he wasn’t loose on campus.
The scenario you have set forth here would make sense of the timeline of events...
They didn't apprehend him although they reported his arrest so he kept going until his mission was accomplished.
IMO, FV