In the Psycho-Pass universe, they don't care as much about catching guilty people, they care more about eliminating people (either by death or rehabilitation) who they see as a threat to their society.
It's also established that in their society has been going on so long that people are so unused to crime (outside people that have identified by Sybil), that they are very unlikely to commit a crime or even really comprehend it. This is shown by the fact that "normal" people have no idea how to deal with any sort of crime if they were to witness one. That implies to me that crime, despite how much its shown in the show, is supposed to be very rare, and most people are pretty incapable of committing one.
People believe that the Sybil system will generally catch people before that point where they are in a mindset where they are capable of committing a crime, and therefore they do not have time to commit a premeditated crime like organized crime.
Lastly, people believe that Sybil will inevitably catch anyone who has committed a crime eventually anyways, since they believe those people will always have a high crime coefficient.
So I assume that most have the most likely erroneous belief that because of these factors, things like organized crime do not exist, and therefore investigations aren't all that necessary anyways.