The Feds were involved because it was their informant that cracked the case, not a CPD informant.

It is highly unlikely that CPD actively investigates the Mob because frankly, there are few mob crimes committed in the city. Suburban agencies do not have the manpower to investigate the Mafia, unless it is responding to specific complaints (i.e. video poker in bars and Prostitution).

In addition to the use of the federal informant, the FBI generally handles all Mob related crime. This is true in Chicago, New York, Philadelphia, Boston and every other major city with organized crime.