This guy should of never been able to get a gun especially if you read what went on when he was in the Air Force. This is why gun laws don't work. You have to have everyone's cooperation in order to make sure the gun laws we have now are adhered to.
The only reason I could think of would be if his sentence hadn't been reviewed and approved by the USAF Jag. Being he was found guilty over three years ago that isn't likely.