[quote=Ghirardelli]
during prohibition, police forces such as Chicago and New York were full of officers taking bribes and pay-offs by mobsters, to either look the other way, fix arrests, court orders or give up information on witnesses.So you could have local police force characters on the take, or conflicted with the urge to take a bribe. or you could even have a mob member on the police force.
[/quote]

Building on this, law enforcement officers had the shittiest wage ever - you could make more money as dockworker basically. I think it's cause of the way they rank up so to say.. you get money based on rank and to get a higher rank you require a few years of work. So head of the PD will earn a shit tonne of money while the actual officers to detectives earned the littlest, shittiest wage ever.

Lets just say that if a mobster or a citizen with darker motives offered them 10 dollars, that was quite a sum of dollars considering you could buy a full evening meal for your family for about 40-50 cents. 

So naturally FEDs would be less inclined to take a bribe - they already earn a good sum of money and they generally hired the good ''idealistic'' kind of person that wanted to hunt criminals because they felt that they were bad guys. Police officers cared less, and just wanted money to sustain their family. 

Later on the PD started hiring more idealistic people and gave them better wages based off a pay-by-caught criminal basis I believe. I could be wrong but this is what I remember.