The Maltese Falcon (1941)
John Hamilton: Bryan
Bryan : Who killed Thursby?
Sam Spade : I don't know.
Bryan : Perhaps you don't, but you could make an excellent guess.
Sam Spade : My guess might be excellent or it might be crummy, but Mrs. Spade didn't raise any children dippy enough to make guesses in front of a district attorney, and an assistant district attorney and a stenographer.
Bryan : Why shouldn't you, if you have nothing to conceal?
Sam Spade : Everybody has something to conceal.
Bryan : I'm a sworn officer of the law, 24 hours a day, and neither formality nor informality justifies you withholding evidence of crime from me. Except, of course, on constitutional grounds.
Sam Spade : [ranting] Now, both you and the police have as much as accused me of being mixed up in the other night's murders. Well, I've had trouble with both of you before. And as far as I can see my best chance of clearing myself of the trouble you're trying to make for me, is by bringing in the murderers all tied up. And the only chance I've got of catching them, and tying them up, and bringing them in, is by staying as far away as possible from you and the police, because you'd only gum up the works.
[turns to stenographer]
Sam Spade : You getting this all right, son, or am I goin' too fast for ya?
Stenographer : No, sir, I'm getting it all right.
Sam Spade : Good work.