How do i start the secret Julius mission in saints row 2?

you go to the police station wich you go to in the son of samidi mission and go into a room and the third floor and it says only staff allowed you go in and will see three 3rd street saints icon mission start if you go into it it says listen in and it will say it for that for the other three icons ones once you do that there is a other room in the bottom left corner of the room your in you go in there and you get dexes number and you call him and he tells you where Julius is