I'm unique for a suspense author in that I don't have a specialty background. A lot of suspense writers used to be lawyers or crime beat reporters. I didn't even know a cop when I started out. I finally figured out that I could visit prisons - I just had to be willing to make the phone calls.
German is more familiar now since I live part of the year in Rome and part in the German part of Switzerland. But it's not difficult to sing in German; it's difficult to feel in German. This takes time. It's a culture.