Williams said he ate his "chicken on the bone" sandwich right next to the sniper's nest on the sixth floor. Why not force him to say he saw Oswald hanging around the nest?
I reckon that Williams did in fact see Oswald in the sniper's nest because why would he go up to the 6th floor to sit with his mates and just plonk himself down in the middle of the floor without checking all the windows?
When Williams went down to the 5th floor he obviously went to the windows directly below the sniper's nest, so what stopped him doing the same on the floor above?

When confronted with the following wall of boxes, would Williams simply shout out to his friends and after not hearing an answer just move on or would he have a peek to see if his friends were there and perhaps just horsing around?

And from the following exchange from Williams testimony, after Ford heard Williams explain what happened on the 6th floor Ford immediately attempt to associate Williams with breaking the law, which could indicate that they thought that Williams was lying?
Mr. DULLES. How much of the room could you see as you finished your lunch there? Was your view obstructed by boxes of books, or could you see a good bit of the sixth floor?
Mr. WILLIAMS. Well, at the time I couldn't see too much of the sixth floor, because the books at the time were stacked so high. I could see only in the path that I was standing--as I remember, I could not possibly see anything to the east side of the building. But just one aisle, the aisle I was standing in I could see just about to the west side of the building. So far as seeing to the east and behind me, I could only see down the aisle behind me and the aisle to the west of me.
Representative FORD.Have you ever had any trouble with the law at all?
Mr. WILLIAMS. No, sir.
Representative FORD.No difficulty as far as the law is concerned? JohnM