Go to the police station (where there is a toll gate with a policeman standing next to it). Hijack any police vehicle. If you hijack a car or do a crime in that area, this will not work. Then, go in front of the gate and wait for him to open it. Once he does, go inside and go straight. Stay in your vehicle. Park next to the garage door then get out of your vehicle. Once out, go next to the building and your will see another booth next to the building. Go inside and kill the guard. Then, kill the booth man next to the gate. Once this is done, go in the garage through the fire exit. Then, go next to a policeman so that he points his gun at you. He should say that he needs backup into his radio. Kill him with a gun. If done correctly, he should be dead, but still standing. Once he gets off the radio, he should fall down and die.