River decision with nut straight- with problems on turn

[flair1239]

UTG is a typical "fish", and CO is Loose Aggressive-Passive.

Please "critique" Turn and river decisons.

Party Poker 0.5/1 Hold'em (9 handed) converter (http://www.selachian.com/tools/bisonconverter/hhconverter.cgi)

Preflop: Hero is BB with 9/images/graemlins/diamond.gif, 8/images/graemlins/spade.gif.
UTG calls, UTG+1 calls, MP1 folds, MP2 folds, MP3 calls, CO calls, Button calls, SB completes, Hero checks.

Flop: (7 SB) 5/images/graemlins/diamond.gif, 6/images/graemlins/diamond.gif, 7/images/graemlins/spade.gif <font color="blue">(7 players)</font>
SB checks, Hero checks, UTG checks, UTG+1 checks, MP3 checks, <font color="CC3333">CO bets</font>, Button calls, SB folds, <font color="CC3333">Hero raises</font>, UTG calls, UTG+1 folds, MP3 calls, CO calls, Button folds.

Turn: (8 BB) 3/images/graemlins/diamond.gif <font color="blue">(4 players)</font>
<font color="CC3333">Hero bets</font>, UTG calls, MP3 calls, <font color="CC3333">CO raises</font>, Hero calls, UTG calls, MP3 calls.

River: (16 BB) A/images/graemlins/club.gif <font color="blue">(4 players)</font>
Hero checks, UTG checks, MP3 checks, <font color="CC3333">CO bets</font>, Hero calls, UTG calls, MP3 folds.

Final Pot: 19 BB

[Hack]

I think raising the CO here would be best.

More often he will have just a 4 for a straight. You have the nut straight, and it will be best a lot of the time against 4 players. If he 3bets it then I think you can call. If he just has the straight then he has to be scared of the flush as well.

Under no circumstances should you ever fold this hand.

You say he's aggressive-passive. If you had a read on him as a passive player and he 3bets it then I would just call here. If he is really aggressive then I would probably cap it.