The worst case was in the subway, when a big black guy talked incoherently in bad Swedish and started to beat on the windows with a crowbar.
I shrugged, walked to the next wagon and called the police. I gave up when I realised they weren't interested in hearing which subway line I was on and what time, so they could meet up with it.
At least they answered that time...
The point is, not long after some crazy person killed a few people with a baseball bat or something outside a subway station. I always wondered if it was the same person. (I didn't see any pictures in the newspapers, which implies an immigrant, like the crowbar guy.)
It doesn't matter if it was the same person, a bunch of violent crazy and/or drugged people will destroy others' lives as long as they are outside.
(As I understand, the Finnish police otoh is well respected and trusted. I don't really know about Denmark/Finland.)