I don't get this....spoilers
...if Robert Duvall heard the conversation, I mean the SAME conversation we the audience and Hackman hear, then he was totally aware that his wife and the other guy were planning something that sunday on that specifically day at the place they mention.
What the heck was he doing at the hotel then? I mean, putting one self on Duvalls's character...I would find it strange, odd, threatening and distrustful to go overthere, knowing the conversation my wife and this other guy had. I would definitely not go alone, or at least I would have carried a weapon with me...
Aside from that, I think Harrison Ford was accomplice of the wife and the four-eyed guy. What do you guys think?
And just for the matter of giving my opinion out, I think that all theories about where the tap is hidden (sax, Hackman's glasses, nowhere, phone) are possible. Don't forget we got 2 "odd" scenes (the man carrying the sax at the con, and the one long shot from the show off of the device at the con) that have no special reason to be there, I mean, no reason to be there, unless the director was to try to tell us something....I just think he just not wanted to give the audience an specific answer about it, he just left the audience to build their own theory about it and discuss with each other about that.
"To act is not to act" - Me