The Justice Department issued a pair of substantial reports this month about the Ferguson, Mo., police department. One carries a message that progressives have been reluctant to accept: that Officer Darren Wilson’s shooting of Michael Brown was justified. The other bears a message that many conservatives have resisted: that the Ferguson Police Department is probably racist and is certainly predatory.

Despite their length — the Justice Department report on the shooting is 86 pages long, and the report on the police, 102 pages — they are essential reading for people who want to understand the awful things that happen when a local government uses its police force as a collection agency.

According to the Justice Department report, the tragic events of Aug. 9 unfolded basically as Wilson maintained all along. About noon, Wilson stopped Brown and his friend, suspecting them of involvement in a robbery that had just taken place (and which they had, in fact, committed).

Brown prevented Wilson from exiting his vehicle, punched him and reached for the officer’s gun. The weapon was fired inside Wilson’s SUV, and Brown then fled. Wilson ran after him. At some point, Brown turned to approach Wilson, at which point Wilson, believing Brown was about to assault him again, fired his weapon, killing the unarmed 18-year-old.

The report’s conclusion is absolutely clear: “There is no credible evidence that Wilson willfully shot Brown as he was attempting to surrender or was otherwise not posing a threat” (page 86).

That report also reveals the poisonous distrust between the police and the largely African-American population of Ferguson. After Brown’s death, a hostile crowd gathered around the crime scene. The investigation had to be suspended temporarily because of gunfire. Chants of “kill the police” were recorded on cellphone video (page 9).

Though Brown’s friend (“Witness 101”) is a petty criminal and his stories were lies, his tale became the public narrative of the event. The Justice Department reports that multiple witnesses, who eventually (and credibly) gave testimony to support Wilson, at first declined to speak, either because they distrusted the police or because they feared retaliation by the protesters.

The Justice Department’s second report explains why the people of Ferguson were so willing to believe Brown’s partner in the convenience store robbery rather than the police. It finds strong evidence that the police and local courts treated blacks worse than whites, although such disparities in treatment do not, by themselves, prove discrimination. For example, the report found that blacks are almost twice as likely to be searched during a vehicular stop, but they are, in fact, 26 percent less likely to be found with contraband during those stops.

That is not necessarily proof of discrimination either, because there might be some other, relevant difference between the blacks and whites being stopped. The black drivers might on average be younger, and the police might be searching them because they are young, rather than because they are black. The key point is that we simply don’t know based upon the evidence the Justice Department report actually provides.

The report does claim that racial disparities remain even after taking such other possibilities into account — and this would, indeed, constitute powerful evidence of racial discrimination — but we cannot be sure because the Justice Department has not published the data it relied on or explained the details of the method it used to reach that result.

What report proves unequivocally, however, is that the Ferguson city government used the police and its municipal court as a means of raising revenue. The city government was very clear about this, explicitly asking the police to deliver large annual increases in revenue generated from tickets and fines.

Not surprisingly, the police responded by aggressively enforcing every provision of the municipal code, no matter how minor or irrelevant to public safety, and the report documents that officers were evaluated based on how much revenue they generated.

Worse still, the city government created vague crimes, such as “manner of walking,” that in effect gave the police arbitrary power to confront and arrest people.

Under the circumstances, no one should be surprised that the Justice Department found a pattern of police mistreatment of residents (I have only scratched the surface in this brief summary) and that the populace came to be so hostile to the police.

The lesson for the rest of us is clear: Keeping our police focused on public safety is best for all of us, and for the officers who risk their lives to protect us.

Joseph R. Reisert is associate professor of American constitutional law and chairman of the department of government at Colby College in Waterville.