I am not sure what gun laws he is supposed to have broken in the previous case. In most states it is not illegal to have two shotguns in your car, or to sell them to another individual.
Here's what the article says...
"He was found with an SKS rifle inside in the car, with five rounds in a clip and one round in the rifle's chamber. Officers also found a sawed-off shotgun and another shotgun inside the car, as well as an ounce of marijuana, a switchblade knife and two shotgun shells on Muhammad."
I don't know about where you live, but in TN, it is a Class C (perhaps B depending) misdemeanor to have a loaded long gun in the car, with or without a CCW permit. That's broken law number one.
He also had a switch blade, another Class A misdemeanor. That's broken law number two.
He had ammunition within the cab for a shotgun in the cab as well, another Class C misdemeanor. Borken law number three.
He had a short-barreled shotgun, a class E FELONY. That brings us to criminal charge number four.
Finally, he had an ounce of marijuana, a class A misdemeanor in TN bringing our grand total to at least FIVE criminal charges for which he was allowed to walk.
Incidentally, it's reasonable to presume that the SKS rifle he was caught with in TN was also the same one used to kill the two soldiers. And, if he would have been on probation, which would have likely been a multi-year condition of his conviction, he would not likely have been in Yemen in the first place.