The shot of the man's lifeless face is actually Amanda Post's doctor boyfriend, Nick, dead on the ground floor - not Judge Stemple upstairs.
During the 1962 flashback sequence involving a younger Amanda Post and her mother, Rita, at home, an unseen figure sneaks into the house and creeps into both bedrooms. When the killer walks down the hallway toward Rita's bedroom, a crew member can be seen standing on the left side of the hallway with their arm stretched across the door frame - in which case, Amanda and Rita should be the only occupants in the house, aside from the lurking killer.