The U.S. has nearly 7 times the population of England. Comparing straight numbers is misleading.
Also, we must rule out 'justified' killings. Cops firing in self-defense, etc. The U.S. guns laws are ridiculously lenient in the U.S. so the American criminals have access to a lot more guns than British criminals. 117 U.S. cops died in 2015 in the line of duty compared to just 1 U.K cop. Adjusting for population, a U.S. police officer is 18 times more likely to die in the line of duty than a U.K. one. It's reasonable to assume that U.S. must act in self-defense more often that Bristish ones.
So, if we want to be accurate instead of hyperbolic, we need to compare the number of 'unjustified' deaths due to police in both countries and adjust for population. I'm sure the numbers are still really sad. And we absolutely need to hold out police officers to the standard of the law, but the numbers provided in the RawStory article are quite skewed and don't show the complexity of the actual situation.