I've received your radical reference question. In order to answer it, though, I will need some clarification in a couple of areas; I'll also start you out with a couple of (hopefully) helpful resources:

a) When you say 'genocide', can you be more specific?
Are you talking about genocide committed deliberately by the United States (and do you have any particular examples here?), or genocide the U.S. could perhaps have stopped and didn't? Or maybe something else? Any examples you can provide here would be really helpful.

b) When you say "the U.S. Government", are you including individual state and local governments, or are you interested primarily in the federal government? I ask because the majority of state and local statistics don't seem to be compiled in a particular place; if there are watchdog groups, they may be specific to individual states or locations.

c) Finally, how far back in history are you interested in going? Do you want to include Civil War fatalities, for example? Or maybe you're just interested in events since Vietnam?

In any case, here are a couple of resources you might
find helpful:

Dealth Penalty Information Center
Since most executions occur within individual state systems, the DPIC compiles a lot of statistics about the death penalty:
http://www.deathpenaltyinfo.org/
(I found this using a site called the Librarian's Index to the Internet, searching for "death penalty" - I had a hunch it existed, and that the LII directory would have it.)

Iraq Body Count
A site that tracks estimates of civilian deaths in the Iraq war.
http://www.iraqbodycount.net/

Police Brutality (Santa Monica College)
This is a "pathfinder" or study guide that may lead you to statistics about police brutality.
http://library.smc.edu/research/topics/policebrutality.htm

A statistical breakout of participation, casualty and fatality data for U.S. wars from the Revolution to the Gulf War.
http://www.cwc.lsu.edu/cwc/other/stats/warcost.htm**
In the time since this reply was posted, the above link has "gone dead." For a compilation of similar statistics, seemingly more, in fact, check out American War and Military Operations Casualties: Lists and Statistics on the Navy Department Library site.

Department of Defense Directorate for Information Operations and Reports - Military Casualty Information
http://web1.whs.osd.mil/mmid/casualty/castop.htm

That's admittedly sort of a mish-mash of sites on different types of fatalities. I found them by Google searching, by tracing links from one site to another, and by using directories like LII. Feel free to let me know which ones are helpful and which aren't.