What happened was that he was trying to smuggle the stuff in his belly instead of in a suitcase...it's not just a coincidence that a guy happened to die on a flight...he was trying to bypass security systems and got himself killed in the act.
I think that he was the owner but he didn't want to have to do the paperwork as he knew that Mexico doesn't allow anyone with firearms, registered or not. So if he went to do the paperwork, he would be told that he couldn't take the gun and he didn't want that.