Street Criminals are NPCs that are programmed to commit crimes. They create a more "complete" environment in the city by simulating typical street crimes making the game more realistic and brutal.
The criminals in GTA III come in two varieties. One of the criminals looks strikingly similar to members of the Southside Hoods, except he has a different face texture and wears a brown jacket, as opposed to the Hoods' red and purple jackets. The other criminal wears a hat, a black shirt with white sleeves, and blue "Camo" shorts and is a white male.
Much like in GTA 2, they will steal any civilian or gang vehicle that they can access, including the player's vehicle. They can also be seen pickpocketing pedestrians, including each other, although the criminals who have been robbed will strike up their fists and stand, who usually run away, or chase and fight them. If the one points their gun at them, they will give them the money that they robbed from the pedestrian.