Because she was with us all in the billiard room doorway while Yvette was screaming, don't you remember?
4 seconds sound clip from the Clue (1985) movie soundboard.
You can hear this line at 01:12:03.146 in the Blu-ray version of the movie.
Quote context
[...]
- What?
- This house belongs to a friend of mine. I've known all along.
- So you could be the murderer.
- Don't be ridiculous. If I was the murderer, would I reveal to you how I did it?
- Well, who else knew about the secret passage?
- We found it, Colonel Mustard and me.
- You found it. You could've known about it all the time.
- Well, why should we believe you?
- But what I don't understand is why was the cook murdered? She had nothing to do with Mr. Boddy.
- I gathered you all here together because you were all implicated in Mr. Boddy's dastardly blackmail.
- Did none of you deduce that the others were involved, too? What others?
- No.
- That's how he got all his information.
[...]