Second, and at least as importantly, the attacker’s firearm(s) were illegally owned.
There are conflicting reports as to whether the attacker had a “Bad Conduct” or “Dishonorable” discharge from the military. A dishonorable discharge is equivalent to a civilian felony conviction and bars you from firearms ownership; a “Bad Conduct” discharge doesn’t necessarily do so.
But in this particular case it did because the incident that led to the courts martial revolved around domestic violence against his wife and child and the discharge was the result of his conviction at the courts martial.
Even misdemeanor convictions for domestic violence are sufficient to bar you from firearms ownership under the Lautenberg Amendment. Thus, barring some sort of specific proceeding that erased that record he could not legally buy or possess a firearm. If he tried to buy guns anyway he should have failed the background check.
Oh, incidentally, it’s illegal to own or buy body armor if you are barred from owning firearms as well.
And yes, the FBI’s records do have military discharge records in them, so if you lie on a 4473 you’re going to get caught.
I’m sure we’ll eventually find out where he got the gun (there are reports he had more than one in his vehicle) but I’m pretty sure I know where he didn’t get it — in a legal transaction post his discharge, and further, when that happened I’m sure his military attorney not only explained that to him he was also likely asked about firearms he owned at the time and told to surrender them.
But, since this jackass was willing to murder he obviously also didn’t care about any laws constraining him from acquiring or possessing firearms either.