I think that he really was the killer of Chris's dad because Tony wouldn't have had to trick Chris into doing the hit. Chris always loved and respected Tony,his surrogate father figure.

Also,Chris would have done the hit just for the increased status in the Family.Being made was OK,but what Chris wanted most of all was to be taken seriously and respected by the guys.

It is possible that Tony thought that,since Chris would do it anyway,he could solidify the bond by telling Chris that the cop killed his dad,but to me,the scene just doesn't play that way when I watch it.

The victim was a long time asset for Tony,and as a former cop,would have still had valuable contacts.Cops never really retire,they just don't go into the office anymore. They still socialize at fundraisers,wakes,conventions,etc.,so info can still be gotten. I really think that Tony actually did something decent for Chris,even if it cost him a PD snitch.