only a moron would think that cops had the power to STOP crime before it happens on a regular basis.
i guess you are under the impression that the police are like superman and can hear someone thinking about commiting a crime and stop him before he does it?
sure you can investigate something based off of tips, but 90% of the time you are answering calls or doing paperwork, detectives are investigating major crimes that have been passed on to them, and the specialized squads are trying to combat crime by busting everyone they can.
none of those cops has the ability to see in someones head. the guy they just walked pas on queen st. is about to rob a variety store with a gun. he didint tell anyone he was going to do it, and is planning on killing the clerk before he robs the place. why didnt the cops arrest him as he walked past? they had no chance to stop this crime.
most anger based, retaliatory crime... assaults, murder, etc.. are not planned, there is no info that can travel to tthe cops. there is no way to stop it.

i'm being realistic. you need to take your head out of your ass.