Rhino answered the other 2.
As for this, Cory (Renner), he's not LE so no point going to a place where he can't win, also he knew who or how many are working there so he waited until the LE had enough man power before going to the mining site after gathering enough info. Plus, he had to go back up the mountain (a shortcut) where Matt's (Bernthal) body was and now it was covered with new snow or the mountain lions took his body and later discovered a trail, leading to the mining site.
Good answer. Understood that he was not law enforcement. Just speculating that he could have followed her tracks while waiting for law enforcement to arrive where she had fallen. Then he could have given a sworn statement which would allow the FBI to get a warrant and go into the mining camp in full force instead of a fishing expedition.
Again, it was an excellent movie. Thanks to you and Rhino for the replies.