Soft-pedalling KK against maniac?

[jtr]

Hello, all.

Played this 2/4 hand earlier tonight. I had only been watching villain (CO) for a few orbits but he gave every sign of being a maniac. He would bet and raise with all sorts of holdings and then fold if his opponent showed strength on the big bet streets.

Here's the hand; the thinking behind my odd play is described below.
Party Poker 2/4 Hold'em (9 handed) converter

Preflop: Hero is UTG+1 with K[img]/images/graemlins/club.gif[/img], K[img]/images/graemlins/diamond.gif[/img].
<font color="666666">1 fold</font>, <font color="CC3333">Hero raises</font>, <font color="666666">3 folds</font>, CO calls, <font color="666666">3 folds</font>.

Flop: (5.50 SB) 3[img]/images/graemlins/spade.gif[/img], 5[img]/images/graemlins/diamond.gif[/img], 2[img]/images/graemlins/heart.gif[/img] <font color="blue">(2 players)</font>
<font color="CC3333">Hero bets</font>, <font color="CC3333">CO raises</font>, Hero calls.

Turn: (4.75 BB) 9[img]/images/graemlins/diamond.gif[/img] <font color="blue">(2 players)</font>
Hero checks, <font color="CC3333">CO bets</font>, Hero calls.

River: (6.75 BB) 6[img]/images/graemlins/spade.gif[/img] <font color="blue">(2 players)</font>
Hero checks, <font color="CC3333">CO bets</font>, Hero calls.

Final Pot: 8.75 BB
<font color="green">Main Pot: 8.75 BB, between Hero and CO.</font>

So, did I mention he was a maniac? When I got KK against him, I was ready to play my hand hard, but the coordinated low card flop disturbed me (weak tight paranoia?). I reasoned that there was a small chance he was actually ahead, or alternatively that his hand was junk and that he would drop if I raised him. So I checked and called all the way, with a plan of check-raising him on the river, except that a scary 4-card straight came by that point. Anyway, for the record I would never play KK like this against a typical opponent. But was it reasonable in this case? Some of you will presumably argue that I should have 3-bet the flop and led the turn, except I'm not sure how I would have felt about a flop cap and a turn raise from this loon.

In addition it seemed clear from his play on previous hands that if his flop raise was just a foolish maniac move, a re-raise from me would see him putting no more money into the pot. I'm really in two minds here, and I suspect that my weak-looking line may win me 1.5BB more when my hand is good.