Two wild stallions were found dead on 10/13/18. Refer to this video from KPNX-TV in Phoenix, AZ (has mandatory ad). Also this story from KPNX and this FB post. There are no suspects at this time and a motive is not known.
The Heber WHT lies within the Apache-Sitgreaves National Forest, about 80 miles northeast of Phoenix, AZ. It appears on the USFS map of WHTs but is not linked on the page.
Western Horse Watchers Association 