IMHO - I'm not a fan of the death penalty, but there's something to be said for hanging horse thieves from the highest tree. I think that was one of the things the Old West had right.
If the theft happened in OK...it is horse theivery...and IS punishable by death. I looked it up...
Make sure to check the sales barns, vet offices...I don't know these people, but keeping an eye on Craigslist helped. They're probably looking to dump the evidence ASAP and may resort to altering the brands...