Yes, most probably the gun came from black market. Germany has the 4th largest gun ownership rate (legal) and a huge black market where you can obtain guns. Though the criteria to legally obtain guns is rather stringent, e.g. must be 18, no criminal record, and must go through psych and other tests.
There are a lot of people like him in Germany. And, that is nothing knew. I recall as far back as 1970s, though at that time they were mostly Turks, and the Germans most definitely didn’t like them. The situation obviously has got worse since then.
knew = new
It was around '92 that my German friend made comments about not liking the Turks.