One additional note.
Even if the shooter was nuts, he was sane enough to gamble.
After the first few bursts of automatic gunfire, the “BOOM” factor would quickly awaken him to reality.
He knew what he was doing and continued his actions for an extended period through changing circumstances.
If he was a meticulous planner, and self-absorbed into weaponry, he likely would have found access to simple crew served weapons which could have caused much more damage.