Initially it was reported that he was “known to police”, a euphemism for “criminal”, and living in Germany illegally after arriving as a refugee.
This has been corrected now: He was “known to police” because he was a witness in a shoplifting while working as a store detective. And he is in Germany legally with a work visa.
Unfortunately, the false info spread like wildfire, and gives ammo to those on the right, even though nothing they demand of the government could have prevented this tragedy.

Completely off topic, but when I lived in Copenhagen 20 years ago, one of the local shops were owned by two Afghan brothers. They were really nice, and we would sometimes talk about current affairs. They were very enthusiastic about our democracy and government. And it happened a couple of times they explained something the government had decided, and how they were absolutely blown away about how clever they figured our government was.
Their enthusiasm about our democracy was quite infectious. 😋

I lived in Nørrebro (North bridge) and it was an absolutely amazing part of town, not despite having many emigrants, but because of it.