Legacy, it looks to me like the rate of decline was more rapid with the blacks than it was with the whites, I see one massive spike i the 80's but that was right around the time of the major crack epidemic, so that would explain violent crimes increasing.
I don't think it's fair to pull a race card on anyone, there is only one race, the human race.. there are factors in class, up bringing, and much more that can determine if someone would do something like this...
How many white serial killers are there compared to black ones? There's all sorts of tangents and arguments that can be made on a slough of levels...