The latch on the door to the “wine cellar” (a small closet-like space within the main cellar) operated only from the outside. There was no passage to the rest of the house from the wine cellar. The broken cellar window was some distance away, in the main cellar, which was actually a warren of rooms opening into each other. If John indeed let himself into the house through that broken window (several months before the murder), he would just have walked around through the cellar up the stairs to the main portions of the house.