I'd be very surprised if a study of the German prison population didn't produce similar results - over-representation of minorities and heavier charges/penalties/sentences for crimes against Germans.
I suspect the statistics are there for the finding.
Well, there have been some, which were to my knowledge a) done years ago, b) didn't come to to such a result.
(I'm only speaking about ehBeth's point No b) here, since that would be equivalent to the quoted study.)
I'll try to find some more recent studies in the university library, which, however, doesn't seem to be easy: we only 'divide' people/citizens according to their nationalty, not so-called "ethic background".
I do have my dounts, however, opposite to ehBeth's suspect, that any German court punishes someone harder only due to the fact of his nationalty, colour of skin etc compared to what a 'white' German would get.
The outcry would go at it loudest throughout the world media - re our terrible history with this.