Probably a waste of time to report it as the people got what they want and aren't coming back to get caught. Yes it is unfortunate that people will kill a deer for horns alone. I think if you don't eat the meat or know someone who does to give it to them, then you shouldn't be hunting. It is possible that they didn't find it till later and decided the meat wasn't any good so just took the rack, but 2 next to each other seems on purpose.