Baja California state prosecutors released grisly details of the slayings but have not yet officially confirmed the identity of the bodies.
Mexican authorities assisted by the the US Federal Bureau of Investigation (FBI) found their bodies in a well in the town of Santo Tomas on Friday.
Thieves apparently killed the three, who were on a surfing trip to Mexico's Baja peninsula, to steal their truck because they wanted the tires.
The latest details in the case come after a fourth body was discovered during a search for the missing men in Baja California.