The Bat very likely is a mental case. And I'm convinced that his crimes are motivated by his mania for personal gain.
6 seconds sound clip from the The Bat (1959) movie soundboard.
You can hear this line at 00:46:49.716 in the Blu-ray version of the movie.
Quote context
[...]
- But in the meantime, Mrs. Patterson, you aren't leaving the house tonight, are you?
- Don't, I'll talk to you in the morning. Goodnight.
- Dale called him at my request. She told me he was coming.
- Who else heard her tell you that?
- There are few killers who kill for the fun of it.
- Now, these young ladies are staying here tonight?
- Yes, they're my house guests.
- Well, when my crew arrives, we'll be busy for a while. So I'd suggest that...
- That we go to our rooms? That's a very good idea. Come on, girls.
- What about a police guard for this house tonight, Lieutenant?
- You've got one. I'm going to cover this place tonight from the attic to the basement.
[...]