But there are just a few police officers who can see what's happening and are prepared to do something about it.
And so the Gangster Squad is born.
Led by Sgt John O'Mara (Josh Brolin) and backed by the honest police chief Carter (Nick Nolte), the squad is an assembled group of crack cops with one aim - to stop Cohen.
Using both brains and brawn, the squad is able to get close to Cohen and start tearing down his empire, piece by piece.
They know Cohen is up to something - something very big - and must stop him before he gets operational or their chance will have gone.
Complicating matters is Sgt Jerry Wooters (Ryan Gosling), a valued member of the team, who jeopardises everything by taking up with Cohen's girlfriend Grace Faraday (Emma Stone).
Grace has the power to bring the entire squad down in a second.
For the squad to succeed it will be a bloody fight to the death. And Cohen is not going to be a man who would lie down easily.
Gangster Squad has a real feel about being transported back in time. The music halls, the clothing, the cars and even the way they speak all point to an era when life was so very different.
This is a violent movie, but it exists within the context of the battle taking place.
Stars 4/5
Cast: Sean Penn, Josh Brolin and Nick Nolte
Running time: 125 minutes
Rating: R16
