Police Brutality

Police brutality is a myth present in some of the games in the series GTA. It is the aggression on the part of law enforcement officials, against the pedestrian or civilians.

Grand Theft Auto 3
In Grand Theft Auto 3, during the mission Kanbu Bust Out, you can hear a man being beaten in a police station, and in addition, when you are inside, you can see traces of blood in it, which implies that there was brutality police there. Therefore, this should be only a game fails because it never gets fully explicit whether or not police brutality in GTA 3.

Grand Theft Auto: Vice City
In GTA Vice City, at police station in Washington Beach, you can find clothes with blood stains in some cells, implying that the police torture detainees so that they confess a crime. But it is never entirely clear, it is never possible to really see some sort of police brutality in Vice City, unless because of flaws in the game.

It is possible that the cells that are considered to be torture cells, are just ordinary cells, where prisoners who go to the police station are housed, and the bloodstains on the shirts could be just drawings or stripes.

Grand Theft Auto: San Andreas
In Grand Theft Auto: San Andreas, in the police station in Los Santos it is possible to find two policemen knocking on a random NPC. This is clearly not a flaw in the game, and is only just a reference to the case of Rodney King, 1992 in LA. It is the only place in the game where you can find police brutality, and it might be used to portray the violent aspect of the city of Los Santos.

Conclusion:
It is obvious that the police in GTA 3D universe acts like a normal NPC in relation to other NPCs, as it will never attempt to arrest them (only the player / protagonist can go to jail). Regarding the NPCs, the police will simply kicks them or spank them instead of holding them, that is, it was not scheduled to arrest people in addition to the protagonist.