User blog comment:Llama919/Possible Beast Titan Identity?/@comment-5774380-20150618200119/@comment-5774380-20150618214536

I think the main clue here is that the Beast Titan was not aware of the existence of the 3D Maneuver Gear or even that he and Mike spoke the same language. That indicates that he's not from within the Walls and that he hasn't had contact with the people within for a long time (if he had contact before).