Invisible Ghost (1941)

At some point in his career, Bela Lugosi probably played someone who is not a murderer, but I am yet to see that film.

In this nonsensical bit of fluff, Lugosi is a respected pillar of the community.  The only whiff of scandal around him is that some years before his wife ran off with another man.

Oh, and the unsolved murders that keep happening in his home.  So you know, nothing major.

As we the audience soon discover, Lugosi's character is the murderer.  But he doesn't know that.  How can this be?  I'm glad you asked.  Buckle in for stupid.

So, for poorly justified reasons, the gardener is keeping Lugosi's wife in his shed.  She was injured in a car crash when she and her lover tried to flee, you see.  And so the gardener has kept her secretly, ever since.  Why?  Well, there's a bit of waffle about how 'it would destroy' Lugosi to see his wife in her current state (she looks fine, but has neurological damage).

However, the gardener's really bad at keeping Lugosi's wife locked up, and she occasionally sneaks out of the shed at night to steal some food from the house. Whenever Lugosi sees her do this, he mistakes her for a ghost, goes into a fugue state, and murders someone.  Why does this happen?  Because that's what the script says it does, that's why.

After the latest murder, the police - who are colossally incompetent throughout this film - arrest the boyfriend of Lugosi's daughter.  The latest victim was an ex-lover of his, you see, who was trying to break up his relationship.  So he had motive, and - lacking an alibi for the night in question - gets executed.  But don't worry, his identical brother will turn up in the very next scene to investigate.

Several more murders will happen, while the police scratch their heads over the baffling "mystery" that would be solved by, you know, searching the grounds of the house where all the murders happen, before things finally get resolved.  My favorite moment of script lunacy in all this nonsense is the scene where one of Lugosi's victims wakes up in the morgue, then dies before he can say anything.  Why does this scene exist?  Your guess is as good as mine.  Perhaps it was supposed to create tension in some way: 'will Lugosi be discovered?  Will he go into a trance and murder the witnesses?'.  That's all I can think of.

The cast does their best with this nonsense, and make it watchable enough if you don't mind how stupid it is, but there's no way to save it from being preposterous.