Consider a drive by shooting happens. You are a cop. You are given description of the vehicle, which includes make, and model and the fact that window was shot out. Soon after the shooting, around the area the shooting took place, you stop a vehicle that matches the description, make and model and a shot out window in the correct area of the car. You see two guns in the car. Suddenly one the occupants of the car takes off on foot. You have no idea if he is armed or not(even though two guns were in the car, it doesn’t mean another one wasn’t on his person). For all you know he was involved in the shooting. What do you? (and keep in mind you have less time to decide than it took you read this paragraph)
Certainly not shoot him because I’m not a fucking monster, and I don’t want to live in a world where cops can just execute people in the street for any reason.
EDIT: “I don’t have enough details to understand this situation, I guess I’ll murder this guy just to be safe” is not an acceptable solution.