You could be right but the lack of skull fractures or bullet holes does not mean the person did not die from a shot to the chest or multiple stabbings.Either way,it’s not a good idea to take a skull because it could belong to a murder victim who was dumped or someone who went missing and just happened to die there because of exposure.
Or, it could be evidence of a graveyard in the area.
Have you ever been to the border country? This was not your typical crime scene. Considering where it was found and how long it had been there the sheriff would have done nothing. If the landowner decided to call the sheriff it was in his hands.