What its saying is that out of the 2000 guys only 120 have been identified and of those 120 about half of them were recently arrived foreigners. The other 1880 could all be Germans or all Foreigners or a mix we don't know as they haven't been identified.
It also doesn't say what constitutes sexual assault, so it could be anything to a guy accidentally bumping into a woman brushing up against her breasts or some creep fondling a chick or straight up raping someone.