Then it must be true. Yes, I must be guilty.
7 seconds sound clip from the Forbidden Planet (1956) movie soundboard.
You can hear this line at 01:33:38 in the Blu-ray version of the movie.
Quote context
[...]
- That machine is going to supply your monster with whatever amount of power it requires to reach us.
- Red-hot. Soon it'll be white-hot then it'll soften and melt.
- Alta, say you don't believe this of me. Tell me you don't.
- Then it must be true. Yes, I must be guilty.
- Then help us, darling. I've known you. I've known you great and noble like the Krell.
- My evil self is at that door, and I have no power to stop it.
- Stop. No further. I deny you, I give you up.
[...]