Factual error: (CONTAINS SPOILERS) Detective Coogan finds an important clue by looking at the photo of Remembrer House, which appears to have been doctored. He is told by the photographer that someone else has the negative, but that the photographer made a "duplicate negative" and can give Detective Coogan a copy. However, this was in the days before digital cameras - and negatives are what happens when you take the actual film in the camera and develop it. It is impossible to make more than one - and even a beginning photography student would know that.