CO has quite a range of hands.

I don't see a straight or draw chase for most players calling a pot-sized bet, although stranger things have happened and the CO is an unknown. Lots of straight draws are out there, though.

More likely I see him on some sort of TPTK or even a set situation. He called the flop on an overcall, so he didn't show a whole lot of strength. The A on the turn didn't scare him at all. The J on the river, if he is now on Aces up, scares him a little because, if he's a thinking player, there's a chance that you just rivered Aces up but he's getting the odds to make the call.

A9 is also not out of the question. On the flop he had two overs to the board and a gutshot draw. I've seen donks draw with less. The A he's figuring on a TPAK. It's bad play, but logical to a fish.

Finally, with everyone limping and some decent odds pf (3.5:1 at the time, works out to 4:1), he might be thinking call/fold pf with something like 97 s/o because he's in late position. Flopped the nut straight, didn't need to push because you were, and let you bet it out. This is a little unlikely, but it happens. If he's L/P, then it fits that character.

PM me the result. I'm interested to see how accurate I was.