US “police” is a large number of federal, state, county, and municipal agencies. So it is no wonder that statistics collection is difficult and therefore imperfect. This estimate is 93% of 1,100 a year, or about 1020. This data does not distinguish between justifiable homicide (criminals don’t always come nicely just because you tell them they’re under arrest) and murder.
Mexican police is notoriously corrupt (see the references to the Wikipedia article). The protests in the article are the result of a massacre of 43 people. When was the last time a US police force massacred such a large group, under orders from local gangs? Would such a massacre have encountered apathy when even a single death can cause rioting?