Well, after stealing all the money in Las Vegas that's the next logical step for a maniac.
6 seconds sound clip from the Ocean's 11 (1960) movie soundboard.
You can hear this line at 01:55:39 in the Blu-ray version of the movie.
Quote context
[...]
- That's good. You're not ill.
- What is it, Mother's Day? Did I forget?
- You dare to be sarcastic after what you've done?
- Well, after stealing all the money in Las Vegas that's the next logical step for a maniac.
- Amazed, aren't you? You probably thought you had committed the perfect crime.
- Mother, who's been talking to you?
- Duke. He knows all about it.
- I mean, why would you believe what Santos says?
- Because, my little amateur thief, he's a professional.
[...]