Need help to find name of a movie

i saw it long ago but don't know its name. the first scene was a veteran cop came into an office and talk to his partner who was also his boss. there was another cop in the room- a young recruit. the veteran treated the recruit quite rude and told him to get out while he was about to talk to his partner but then his partner let him know that this young recruit was his new partner.

the veteran and the recruit came out the office and people outside laughed at the new recruit and sticked a paper on his back which wrote a mocking word. the veteran saw it and yanked it off, the recruit knew nothing.

after that, in an arrestment, the veteran asked the recruit to watch out a criminal and could shoot him if he had any suspect action while the veteran checked out the evidences. the criminal tried to escape but the recruit was too afraid to shoot. the criminal got free and shot at the veteran.

the recruit was so regret and tried to trace for the criminal, at the end of the movie when he pointed his gun at the criminal again, the criminal said he couldn't pull the trigger but he laughed and shot.

the last scene was the recruit came into an office and saw his partner was with another young recruit and everything happened just like at the beginning.