i believe they only kill with a purpose or if provoked... that's not to say an outcasted beta male won't scoop up your family as a snack
the invisibility/camoflauge abilities are very intriguing.. most people report them having telepathic or infrasonic abilities
with the low frequency infrasound, some say their whole soul was permeated with a sinking feeling worse than any dread imaginable.  others say they had entire "mind speak" conversations with them
if they have this sonic ability it could explain their invisibility. sound waves interact with photons and can change light wavelengths
just like infrasonic frequencies are just below our audible spectrum, they might have a way of cloaking themselves outside of our visible spectrum 

 either themselves or entire light fields
they could be more sophisticated than humans. they likely live at least partially underground in the first place... wouldn't be shocking at all for them to bury their dead.
not to mention you have hunters who been out in the woods decades and never seen basic shyt like a mountain lion carcass
damn you know its real cause the dogs
did you feel anything unusual from it screaming?[/QUOTE A lot of times the neighborhood would say, wherever it snowed...  you could hear it crunching from the woods and would roll up straight to the houses and bash the walls of a house, shaking the whole thing.  Big rocks being thrown at the dogs, but the dogs were never dumb enough to go after whatever it was. 
     From what the old ones would say about him/it.  The Bigfoot/Sasquatches are Medicine/Witches men or beings who can make themselves invisible.  Walk through worlds, shift to a different plane.   The Story is when everything was going to hell, some natives were able to turn themselves into these beings.  Wherever they show up the whole energy of the place shifted, dogs go nuts, everything gets quiet.  They definitely won't show themselves to White People, or only when they're by themselves... and someplace their not supposed to be.