I don't think skinning a buffalo is a one-person job... or a job for the inexperienced, no matter why they did it. That doesn't mean an idiot couldn't try it and botch it up, as I've seen more than my share of deer hunters who screwed up a good cape. It would be interesting to know if whoever skinned the animals did a good job, and that should be evident from the carcasses. If it was a pro, a taxidermist or someone with experience at bison slaughter it should be obvious; the skill with which it was done would narrow the range of possibilities of who did it.
I heard of a case some years back where a museum had acquired a bunch of bison skulls and had a volunteer do the messy job of cleaning the skulls so they could be used on posts around a dance circle for an upcoming pow wow at the site. The intention was to store them after the pow wow for future years events, but the skulls were snitched by a "medicine woman" involved in the sponsorship of the event {and her relatives} and sold to some collectors in Europe, last I heard. The museum was too politically correct and too afraid of the woman ginning up protests against them because her family was already developing a reputation for race hustling, so the museum did not object, and the thief was able to pocket the proceeds the Chicago way. To her the buffalo was no more important to her spirituality than it was to the commercial robe hunters of years past, though she talked a good game pretending to be a shaman.
The point is, is that if someone skinned them and left the meat, they weren’t up to rustling.
This was symbolic to someone.
That's a good question. It's certain that whoever did it wanted something more than to simply kill the animals. That would be quick and easy to do. Skinning one in situ is a risky proposition.
As for fake shamans; lots of those around in every tradition.