Many factors come into play. Is it law enforcement with body armor? Is the attacker going up against those who are armed? Is the attacker using FMJs, soft points, or hollow points? How many rounds does the attacker use per victim? Where are they aiming for? What is the quality, stopping power, and expansion capabilities of the bullet? How many joules does the bullet have? What is its velocity? What is its mass? What is its diameter? What range is it being fired from, and will it retain its energy? How much time does the shooter have and why? Could it evolve into a hostage scenario?
I could go on and on, but the point is that a simple shooting has a massive amount of variables, let alone a major one.