[tigerite]

I like the line. Especially on the turn to check behind as you have outs to the 2nd nut straight. He gave you the chance to get a cheap showdown, I don't see the harm in taking it. As for what he had I would say either some kind of draw (JT spades, maybe?) or QJ. I think AQ would re-raise you on the flop. I guess it's possible he has KQ, checks the river thinking you have AQ and will bet so he can check-raise. Hell at this level it could have been AK whiffed til the river.

I would think JTs he would want to at least get some guaranteed money in on the river though, so it's probably the least likely.