You observe similar criminality trends in African immigrants to Japan compared to the other immigrant groups (including Europeans and Americans), for example. The only exception is the Brazilians, who were brought in as low class workers, have a MUCH higher crime rate, have trouble renting outside of low-income areas, can't get high class jobs, and are generally treated like criminals on-sight.
Germany has a similar problem with their Turkish population.
And it's not restricted to skin color, either. Low class culture takes generations to clean out. I've had a number of dealings with shady descendants of American-Italian immigrants, many in high level financial market jobs. This is fallout from the exclusion of Italian immigrants from the higher classes in the early 20th century, which led to an undercurrent of criminality in their culture (not to mention their good positioning during alcohol prohibition, gambling prohibition, and later drug prohibition).
Cultural currents take multiple generations to steer, which leaves one with many chickens coming home to roost after treating a class of people like shit for so long.
I am Italian and I can assure you that those who remained in Italy are not different. Large part of the Italian immigration to the US comes from the south, where the different types of mafia are only the official and extreme degree of a widespread culture of corruption, shady dealings and reciprocal abuse.
Edit: I know HN guidelines say not to complain about moderation (I've been here for 13 years now), but it's ridiculous a very simple, on-topic question should be downmodded into oblivion on a site whose purpose is discussion. While I have karma to burn and will happily keep participating, I'm concerned that this trend will have a chilling effect on people who do not.