Ok 1st post. Time to stick my neck out. We'll see if it gets past the mods ;>)
Evidence: Isn't the thousands of eye witnesses reports from decent everyday folks (who never asked to see one of these things) enough evidence? It is for me.
Proof: So I read that as a dead body of whatever these things are. I tend to think they are less like primates and more like us than we want to think. Killing becomes a different thing when they have features like ours. Also, it would seem these things outclass us in just about every way. We are not talking about dropping a huge bear. What makes anyone think they travel alone? IF you could successfully execute one, what makes you think their clan/tribe/pod would allow you to have the body let alone your life? Seems like a bad idea.
I believe the governments know full well about these beings. They don't want us to have proof. That's why all of those folks who didn't ask for an encounter are ridiculed when they tell their truth. A body won't change that.
I am an attorney and realistically, I do not believe a jury would convict you for shooting a BF, particularly since the public primarily sees them as "monsters". Also,
It would not be difficult to prove self-defense since you could say you were in fear for your life. I doubt that any DA would pursue prosecution unless the DA wanted the publicity, but it might turn out to be bad publicity or ridicule.