Hmm, a black peice was captured on a3 before the Bishop or Rook on the Queen side escaped, and it can't have been the missing pawn because those are the only two missing White pieces and as a result the pawn can't have captured to the a-file.
So knowing this, it must have been the missing Black bishop that was captured on a3. But that is not possible as a3 is a dark squared and the missing one is a Light squared Bishop. That is, unless the rook on h1 is actually the a1 rook and the original h1 rook was captured on the a-file by Black's b-pawn which was subsequently captured on a3. Since this is the only possibility, the knight must have moved in order for the h1 rook to escape, and the a1 rook to take it's place on h1.
Knowing that there are no promotions in the game, prove that the white king's knight has moved in this game.