Wonder what Mexican authorities would have done to this murdering pervert if he and the family had stayed where they belonged?
Having dealt with Mexican Police, both Municiple and Federalies (Judical Police) I'll take a stab at answering your question.
If the father or one of the uncles (maternal or paternal) were to stab this POS within a few hours of the discovery, then "Nobody saw Nothing".
Unless the family (of the victim) had money, even a couple of hundred USD), for you see the law has been broke and a price must be paid.
If the family of the Avenger were to have serious money - i.e. a bunch of relatives working in the USA, then the moditha extracted would be greater.
If the POS's family had serious money, then it gets interesting. Everyone would go to jail in the (child's) victims family. Someone would be expected to 'man up' and do a few years in a prison - and everyone would take pride in making the life of the prisoner more comfortable (i.e. bribes to guards - family - contact visits) But the family would gain great status in their community - i.e. don't screw with them - they have killers at their disposal. Very macho thinking ya, but it's Mexico.
All comes down to how much money can be had by judicial authorities....
Remember, the Mexicans wanted 'Dog" Chapman - the bounty hunter to do serious time as he had embarrassed the corrupt system. (And Dubya was willing to throw him to the wolfs)