The advocates reported that the horses were shot in the abdomen, face and between the eyes, according to the story by KPHO News.
Shots to the abdomen may have occurred from longer range, to make the animals approachable, with kill shots applied at short distance.
Where do you find expertise in killing wild horses by gunshot? At wild horse roundups, where it is often associated with pre-existing conditions.
The method was sanctioned by PIM 2021-007, Euthanasia of Wild Horses and Burros Related to Acts of Mercy, Health or Safety.
From paragraph VI.2 in Attachment 1:
A properly placed gunshot to the brain of an animal that is calm and still, or humanely restrained, instantly produces an unconscious state followed quickly by a painless and humane death. This method of euthanizing wild horses and burros requires only minimal handling and restraint; and when performed on the range, drug residues that may poison wildlife are not a concern. Only qualified and experienced persons skilled in the safe handling and use of firearms and trained by a veterinarian will perform the procedure. The optimal placement of a gunshot is from the front of the animal, perpendicular to the skull at a point one inch above the intersection of two imaginary lines drawn like an “X” from the eyes to the base of the ears. Typically, when euthanizing a wild horse or burro in this manner with a handgun, the animal will be approached to within five-to-six feet and the gun will be held within a few inches or up to two-to-three feet from the animal.
This information is not limited to government contractors or the agencies that hire them. The image above was found at thinklikeahorse.org.