Here are more excerpts from the Washington Post article addressing your concern:

Typically, activists and the media measure police actions against population ratios. Given that blacks are 13 percent of the nation’s population, a 26 to 28 percent black share of police gun fatalities looks disproportionate. 

In America's 75 largest counties, comprising most of the nation's population, blacks constitute 62 percent of all robbery defendants in 2009, 57 percent of all murder defendants, and 45 percent of all assault defendants — but roughly 15 percent of the population in those counties. 

Police critics have never answered the question of what they think non-biased policing data should look like, in light of the vast differences in rates of criminal offending. Blacks commit homicide at nearly eight times the rate of whites and Hispanics combined. Should police stops, arrests and those rare police shootings nevertheless mirror population ratios, rather than crime ratios?