The FBI does collect crime data, but its not perfect. Its called Uniform Crime Reporting (UCR). I think its all available online.
After lots of reading and reflection, I think a lot of the crime is due to the culture of poverty and the uneven/unfair application of law enforcement in big cities. The Broken Windows policing strategy used in alot of those places has eroded respect for law enforcement and the rule of law in general. Selling a cigarette or drinking a beer on your porch will get you sent to jail just as quick as robbery or dealing drugs. Those people bitterly distrust the police. They have little hope of succeeding in life in the first place. Each time they are arrested and sent to jail for loitering in front of their house while waiting for a cab, they lose a little more hope and become a little more bitter.
I suspect it is the opposite or a combination.
When people respect the police, cooperation goes up and crime goes down.
When people do not respect the police, cooperation goes down and crime goes up.
Not enforcing the law breeds disrespect, violating the law breeds disrespect, selective enforcement breeds disrespect.
Urban crime communities can suffer both ways, insufficient policing and policing that is unjust. It is a tough job to be a police officer in an area where you are not trusted.
A welfare family of 4 can obtain more than 60k annually in handouts. I wager most older freepers grew up with far less and had parents that worked hard and paid taxes, yet lived with little to show for it. Still they never thought of committing crimes. African culture is the same in many other countries.