Carl Johnson got an inscription at LSPD but he has no experience. Since he knew a guy who had a suit, you must go and rob it. Then resolve a crime to get on the records, kill the "Beard's Gang" leader and the rest of the team.
Afterwards, well he is a gangster, not a cop so you will have to infiltrate the Police Department and rob two bags of money killing everyone with your Minigun, then escaping to Grove.
Difficulty: Hard (maybe Very Hard)

Good Luck! :D