Murder rate in the U.S. is 4.7 per 100,000, or about 0.005%, or one-half of one-hundredth of a percent.
http://en.wikipedia.org/wiki/Crime_in_the_United_States
In other words, cops are killed at double the rate of civilians.
At least according to the easily available statistics I can find.
Thanks, you saved me looking it up.
CC