JJ on KKxxx vs passive.

[Pog0]

I don't think there's much to this hand, but since the converter doesn't work for the site I play on and I've already manually transcribed it, might as well look for confirmation. Are you bet/folding, bet/calling, or checking behind to an unknown here.

Argument for checking behind is that calling a c/r seems out of line, but since he's unknown, he could very well c/r bluff this river (allbeit infrequently). Is this infrequent risk of being c/r with either a bluff or K big enough to just check behind... considering there are very few hands that should be calling this river that I beat. By the time it got to me on the river, I thought that the most probably hands for him were
1. Busted flush draw
2. Slowplayed or scared king
3. Low PP, A4, random junk

1/2 8-handed Poker network

Hero is Button with J[img]/images/graemlins/diamond.gif[/img],J[img]/images/graemlins/club.gif[/img]
Villian is new to the table and virtually unknown (although obviously loose)

PRE-FLOP
(4 folds), CO calls, Hero raises, SB folds, BB calls, CO calls.

FLOP (3 players) K[img]/images/graemlins/heart.gif[/img], K[img]/images/graemlins/spade.gif[/img], 4[img]/images/graemlins/spade.gif[/img] (6 SB)
BB checks, CO checks, Hero bets, BB enacts all-in protection for the 6SB, CO calls.

TURN (2/3 players?!) 3[img]/images/graemlins/diamond.gif[/img] (4 BB)
CO checks, Hero bets, CO calls.

RIVER (2/3 players) 7[img]/images/graemlins/diamond.gif[/img] (6 BB)
CO checks, Hero?

Bet/fold right? If the river was 7[img]/images/graemlins/spade.gif[/img], check behind right?