Chris later alludes to the incident in a much later episode--the one where Tony calls Chris to a secret meeting, but Chris falls asleep after hanging up as he is stoned--I didn't record the season, and as it doesn't come out 'til November 3rd over here, I can't say which ep exactly. Or it may have been the one in which Chris is sent to rehab. However, Chris said that he appreciated what Tony had done for him; I think it was something like: "I'll never forget what you did for me with that cop who killed my old man." So no, Tony didn't tell Chris that it wasn't him--assuming that it wasn't.

My guess is that the cop--whoever he was--owed Tony money and simply wasn't paying up (or something just as worthy of being whacked). Tony saw it as the perfect opportunity to motivate Chrissy and close a hanging demon over his head (who killed his dad?) and it was the perfect way to get rid of the cop--who may have decided to try and blackmail Tony and rat him out so as to avoid a backlash for not paying up.

Mick