So the 6% is a better measure of the national proportion of crimes committed by aliens (legal and illegal).
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I don't know what the final number is. However, just so that you understand what you have just said--its appropriate to point out that if you take 6% and multiply it by the federaly provided total number of murders-- 16692 for 2005... you get 1001. If you multiply that by 4--which is the number of years the USA has been involved in Iraq--you get a number that is higher than the total US casualties in Iraq.
That was also the point of
this article posted at FR. I have no quarrel with your comment here — 6% of 16000 x 4 years = more people killed in the US by aliens than Americans killed in Iraq. I would quarrel with figures of 20-27%, which come from looking at federal prisons only, and not at the figures from the very same source that does tally aliens in all prisons.