It was revealed later that the killer drank tea from a decanter and pretended it was whiskey while he remained sober.However, on the night of his mother's murder, he drank whiskey from the same decanter as he policeman. So they would both have had to have been passed-out drunk, since it was whiskey.
Towards the end of the movie, the caretaker named Seth was stabbed in the throat and put into a coffin. However, when the coffin is opened, there is the face of a different actor with the throat wound. Apparently, the actor portraying Seth refused to lie in a coffin.