There's an enormous gap between justice as its administered in our courts and "justice" as it is meted out in the thousands of fatal encounters with police that take place in the US every year.
The US is the only western nation that currently enforces the death penalty. Thirty-two states and the US federal government apply it; 18 states and the District of Columbia do not. There were no legal executions in the US between 1967 and 1977. Since then, more than 1400 convicts have been executed, an average of about 40 people per year (just 20 in 2016, a 25-year low). The death penalty has not been shown to decrease murders or other crimes. The murder rate in non-death-penalty states is consistently lower--30 percent on average--than in death-penalty states. Nonetheless, capital punishment in the US retains strong popular support.
As you would expect, the death penalty is only applied for very serious offenses. These vary from state to state, for example intentional homicide with aggravating circumstances such as rape, multiple victims, or the killing of an on-duty police officer. At the federal level, treason, espionage and large-scale drug trafficking are also capital offenses. The constitutional right to due process guarantees that even after a fair trial, conviction and sentencing, convicts facing death have access to legal appeals that can delay their execution for years--currently an average of more than 14 years.
None of the above is true on the streets:
--As multiple notorious cases have shown in recent years, a fatal encounter with police can stem from a broken tail-light, shoplifting, carrying a crucifix, or as minorities have been reporting for years, walking or driving while Black, Hispanic or Native American.
--As a depressing number of videos show, "due process" is often reduced to minutes or even seconds between an officer's first contact with a suspect and a fatal barrage of shots.
--Fatal encounters with police are far from fair with respect to race or ethnicity. A recent study in the American Journal of Public Health analyzed 2,285 "legal intervention deaths" in the US between 2010 and 2014 and found that Blacks, Native Americans and Alaskan Natives were 2.7 times more likely to die in police encounters than Whites, and Hispanics 1.6 times more likely to die.
--The interactions between police and the people they are supposed to serve and protect vary greatly from state to state. Police in New Mexico, with a population just over 2 million, killed 28 people in the first half of 2016. Nevada, with a comparable population, saw just 4 police-related deaths. Arizona has a slightly smaller population than Washington, yet Arizona police killed more than twice as many people. Californians are three times more likely to die in an arrest-related event than New Yorkers.
Of course, this does not mean that all or most of those deaths are illegal or illegitimate. Police officers do represent the front line of our system of justice, place their own lives at risk (although not nearly as much as the public believes), and have to deal with many difficult and sometimes dangerous people and situations. University of South Carolina criminologist Geoff Alpert points out that in 98.9 percent of cases, killings by police are found to be justified.
However, justified does not mean necessary or just. The number of police killings places the US at the ragged edge of other developed countries. A few examples:
The US has about 6 times the population of England and Wales. Yet US police killed more people in the first 24 day s of 2015 than police in England and Wales over the last 24 years.
The US has about 4 times the population of Germany. US police kill two or three times as many people every week as German police do in a year . Almost twice as many unarmed Black men (19) were killed by US police in 2015 than all the people killed by police in Germany that year (10).