Kill Mafia spies before they kill you. One group is on the island in the pond in the park. The second is one block up from love media and the third is on the building across the road from the casino.
Note For the first group you don't need to go in the park you can stand on your car roof and shoot or off the bridge to Shoreside Vale. The second is easy, just blow up the van and the third you must go on the roof of the casino and shoot across the road.