Just before the first ramp leading down into the underground section of the carpark, there is a roof top with a small shack on it. The roof is accessed by jumping upon the grey dustbins stacked against the wall. It's then possible to shoot your way inside. Drop down the hole and you will end up in a room with the body of a dead mobster, some sniper ammo and a radio. Turn it on and you will recieve a message from Remedy. There is also the Rockstar Games logo on the wall.