Although I write in this commentary solely about the building in which the horrible crimes are happening, notice that this is already a spoiler - if not THE spoiler of the whole movie. This is why I "flagged" this text.

It is not by change that the candidates for "haunted houses" are exclusively old buildings. "This house is history, and you are a part of it", the maintenance supervisor says in Tobe Hooper's "Toolbox Murders" (2003). Practically only old houses possess these creaky beams, that stale odor that comes out of the walls, the characteristic noise when the wind presses against the windows, the howling of an old elevator, etc. But that is not all. Before the unfortunate functionalism started to make Tabula Rasa with each trace of architectural generosity, houses often had strange hollow parts in the walls, little closets that lead wide into nowhere, "crawling spaces" between ceiling and next higher floor, mysterious huge and sometimes more-level attics and cellars, etc. And so it is in "Toolbox Murders": "There is a whole townhouse in this building", the historian in the movie says. It turns out that from each apartment there is a little space lacking, but so that these parts are connected by a steep stairwell in the wall of the house. (Note: The building is not the Ambassador Hotel, as indicated in IMDb. The Ambassador Hotel was torn down two years before the movie was shot.)