I'd expect better from Hacker News.
For what it's worth, Wikipedia has a complete list of people killed by US Police Officers and the police reports from them. In 2012, there were 587 people killed by police [1]. This is much, much larger than in Germany, even accounting for population difference.
I would argue that more relevant than pure population is differences in homicide rate. By the data you've given, approximately 1-2% of all homicides in Germany are by police officers (6-12 officer killings, 690 homicides in germany [2]). It's worth noting that in the USA, approximately 3% of all killings were by police officers (547/14748[2]) which seems in line with what my understanding would be -- it's worse in the USA but not ridiculously disproportionate.
[1] http://en.wikipedia.org/wiki/List_of_killings_by_law_enforce...
[2] http://en.wikipedia.org/wiki/List_of_countries_by_intentiona...