SO, since I just replaced all my logs with new ones, it happens to be very easy for me to check this. And this gentleman from Germany has left no physical log for any of our caches that he has claimed. And he has claimed to have found 9 of them. I expect that he may not have signed the log for any of the 43 NYC caches that he has claimed.
Now I can easily delete his logs. But shouldn't we all complain to Groundspeak about such a Geocacher?