There is knowing, and then there is letting yourself KNOW. Having been in LE himself, no-one will EVER convince me that GA did not know exactly what that smell in the trunk meant the minute he smelled it. PERIOD. He can backpedal all he wants but there is no mistaking a rotten pizza smell and the smell of death. Decomp has a very distinct, bad, rotten fruit, but funkier, nastier smell. Old nasty pizza smells completely different. I think he knew, but didn't want to and kept his opinion to himself because what it meant was too damn horrific to process.
As for CA, she may have strongly suspected, but I think that day of the interview was the first time she had allowed herself to KNOW KNOW. That is why we see a numbed, silent, defeated CA. What we saw, was the pause in between, while switching gears from the still hoping gramma, desperately searching for her precious Caylee to the damage controlling, venom spewing, true color showing person we see after this point in time. Once she let herself KNOW KNOW, there was no more reason to put up the supportive mom, worried gramma, nice lady, please help me find my babygirl front.