What he did have was a past that should have been a warning for those he dealt with. Two gun infractions, yet he evidently was still able to buy the shotgun he used. Sounds to me like he is the product of a justice system that is broken. All the gun laws in the world don't do you any good if you don't enforce them.
I had one of my sailors who married a psycho mexican girl. She was literally nuts. He called the police one night because she went wacko. In the end he pled guilty with her on a minor domestic to avoid having her go to jail. He finally divorced her after she put on her wedding dress one night and buried a knife in her own stomach.
My sailor jettisoned the psycho, but he was stuck with a Lautenberg problem and can't own a gun, meanwhile the Navy Yard shooter has two arrests involving reckless gun use and evidently was still able to purchase the shotgun.