Cops don't really stop murders, they at best arrest the guilty after the murders have been done. But then if you actually look into the number of murder cases that are solved, it turns out they kind of don't really even do that very well.
goddamn i love how effortpost replies pile up from hexbears in response to unthought regurgitations by liberals, we've got the best posters folks, many people are saying this
cops don't stop murderers, in the vast majority of cases, (all crimes not just homicide) they turn up afterwards.
they direct CSI and then hand over the case to homicide detectives (who are under pressure to deliver results like some kind of salesman, but that's another conversation)
less than 0.3% of officers are in homicide to begin with.
It's a bad example, and you'll be hard pressed to find a good one that proves your point. Cops (in the US at least) rarely prevent crime before it happens. Hell, their investigations after the fact rarely even result in convictions. Most of the time a cop is involved with something, it's because another cop asked them to. A very very very small portion of their work hours goes towards actually responding to crimes in progress.