Flip the situation...
Mexican crosses the border by accident with illegal firearms...
Oh' Wait...
I would not jump on the bandwagon too soon. If it was a Mexican going north he would be held for trial. It just takes longer in Mexico. This was his 4th time crossing. There are signs indicating that the border is the next and last exit. Who is to say that this guy has not been bringing guns for sale in Mexico for a little extra cash. When were these guns bought? How many has he bought lately? I live close to TJ and a local American on the Baja Image committe has visited him at least 3 times and said he was in good health. This Marine could be lying and maybe not.
If he has crossed 4 times, he knows the rules. He confessed before they searched but if he was not stopped would he have gone to the police and confessed. I cross twice a week and there are random checks if you get a red light you are required to pull over into secondary for a search. There are also agents who pull over most trucks or vans if they peer in the vehicle and see too many boxes, they will point you to secondary.
The Mexican legal procedures take a long time. Mexican suspects are treated worse. There is no NCSI TJ. There is not even a fingerprint database in Mexico. They usually just beat you until you confess to something