There are many ways to become a Grand Theft Auto 5 cop in the game, but one of the most popular ways is to earn money by robbing and stealing. There are many different missions in the game that can be done for money, and some of the more common ones include driving around looking for targets, or taking down rival gangs. There are also side missions that can be done for money, such as robbing a bank or stealing from a rival gang leader. The best way to make money in Grand Theft Auto 5 is to do as many different missions as possible and find new ones that will offer you high rewards.