Roommate moves out, does he owe?

[rwanger]

The scenario: 3bdrm apt, 1 roommate is moving out, a semi-random person is moving in. 6 or so days before the move out, you say to the guy moving out: -Hey, me and the other roommate were thinking about getting a cleaning service to clean this place up so that the new guy doesn't have to move into someone else's filth. Want to pay $20 and we'll split it 3 ways?-

He replies: -Yeah, that'd be great. Then I won't have to bother doing any cleaning.-

Sept 4th (72 hours after the roommate has left) the now gone roommate calls to say -I just got the last bill, you owe me $48 for the utilities.-

You reply: -Okay, do you want me to subtract the $20 for cleaning?-

Roommate: -Ummm, what are you talking about, that's the new guy's responsibility?-