If you are a criminal and you acquire a weapon, you can shoot at police but all the police can do is try to hit you with a hammer whilst attempting to dodge a barrage of bullets. If the cop attempts to use any type of weapon against the trigger happy criminal, the cop gets demerits.
This is just one of the reasons City RP sucks.
Yep, and more on that subject.
Even if the cop COULD shoot at the criminal, it would be to no avail.
You can't weaken him to slow him down, infact your bullets will help push them further back.
You can't kill them, or else they'll be back at their spawn, get their buddy to spawn some stuff and bam the guy is outside again killing.