The second movie sounds a little like “Gaslight” in which Charles Boyer tries to make his wife, played by Ingrid Bergman think she is losing her mind. I don’t remember it including anything really gruesome though.
I don’t know of any website like the kind you want, but you might have luck just asking in some movie website forums.
I once asked a friend if there were reverse dictionaries, where you could find out if there was a word for what you wanted to say, She said there were such guides, they were called “parents”!
That movie even made gaslight a verb.
“They are trying to gaslight her”.
Great movie.
The American Film Institute had decade long indexes with synposis (often taken from pressbook materials) for some decades (1920s, 1960s). Sometimes they could be found at the public library.
IMDB has a plot keyword search option that is similar to the index in these books.