I'd also say it's not a genetically pure European Wildcat. The tail isn't quite right - not as bushy and thick as in a pure-bred Wildcat and it looks a bit too long to me, the tip isn't blunt enough, the markings aren't quite distinct. The stripes on the body are typically more distinct as well, and the eye colour would be highly unusual for a European Wildcat, their eyes are typically yellow. Possibly a hybrid, or just a very nice, muscular domestic cat.
For more information have a look here:
http://www.scottishwildcats.co.uk/identify.html I find that website pretty useful. You might also try to post one of your pictures to the "Mammals" section on Birdforum, there are quite a few people who know their mammals very well.
By the way, the population in Germany seems to be doing quite well. Doesn't make it a lot easier to actually see one in the wild though. I only managed a couple of sightings in the past 25 years or so.
Hermann
