I can't prove it yet, but we both...
3 seconds sound clip from the Batman Returns (1992) movie soundboard.
You can hear this line at 00:45:43 in the Blu-ray version of the movie.
Quote context
[...]
- Shows what you know Mr. To-the-manor-born-with-a-silver-spoon.
- Oswald is Gotham's new golden boy.
- If his parents hadn't 86'd him, you two might have been bunkies at prep school.
- Oswald controls the Red Triangle Gang.
- I can't prove it yet, but we both...
- Wayne, I'll not stand for mudslinging in this office.
- If my assistant was here, she already would have escorted you out...
- Anywhere he wants. Preferably some nightspot, grotto or secluded hideaway.
[...]