I think the ''visitor'' belongs to the family of the wood borer beetle, it was way larger than it looks on the photo, about 3/4 of the size of my index finger and it was equipped with strong looking mandibles, perfect for gnawing wood. Yeah, the robber fly is pretty brutal, it injects tissue-dissolving chemicals into the still living prey which makes it even worse than the Alien Like making a smoothie and then drinking it with a straw.