In his late teens, a cousin of mine I’ll call Burt was traveling, by car, to Mexico with some friends. On the way, they met another group of kids with their own car, who wanted to go along–however you do that with two cars.
These other people were stopping at salvage yards all the way to the border, where they were selling parts they were removing from the car. When they crossed into Mexico, they went to a salvage yard there and tried to sell the car itself–and were promptly arrested when it turned out the car had been stolen and it was on a hot sheet. (Moral: Mexican salvage-yard operators are not fools.)
My cousin and his friends were also arrested; with the others, he was put in jail in Tijuana. The jailers sent a letter to his mother, my aunt, in central California, saying that she would have to bring $500 in cash to get Burt released. We suspected that if she did so she would wind up in jail, too, and they would take her money. She called the American Consul office in Tijuana, and got Burt released without her going anywhere or paying a dime.
Please post your comments, or your examples of skirmishes with the law outside the United States.
No comments on your question, but I will say that I often deal with law outside the United States. After all, I am a Canadian lawyer. 
Probably not what you wanted to hear.
More seriously, I have counselled clients as to what happens when they cross international borders. Such things as, they are subject to the constitution and laws of the hosting country–the constitutional protections they are used to at home do not necessarily translate to the foreign hosting country. Something similar may be in place, but there are no guarantees. Regardless, I always advise that they not chum up with people they meet on the plane, agree to take packages for others across international frontiers, etc.
That being said, I cannot advise as to what, legally, ought to happen in your situation. The best I can advise is to get a Mexican lawyer, who can help you through this. The American consulate can give you some suggestions for local Tijuana lawyers licensed to practice in Mexico, who can help.