Hanging horse thieves had less to do with the theft than the likelihood that stealing someone’s horse out on the plains would result in the death of the person whose horse was stolen—before the discovery of the Oglala aquifer in the 1930s and the creation of reservoirs later in the 20th century, being afoot on the plains could leave you days or weeks away from water, not to mention exposed to the other dangers (like marauding humans).There were not a lot of horse thieves roaming around back 100 years or so ago for some reason.