He had the shotgun cause he was going on a hunting trip to Costa Rica.Mexico is one of THE MOST CORRUPT, CRIME-RIDDEN, DANGEROUS countries on the planet. Anybody who goes there is an IDIOT ! And WHY did he bring this shotgun with him in the first place ?!
I hope he gets out soon, but his own stupidity put him where he is.
And in most countries if you are bringing in something that is legal in your country but illegal in the country you are going to and declare it, all the Custom people do is take it away from you and give you a lecture not to do that again.