Ferguson Officer Darren Wilson is pictured in this undated evidence photo.

WASHINGTON/KANSAS CITY, Mo. — A U.S. probe found systemic racial bias targeted Blacks and created a “toxic environment” in Ferguson, Missouri, but cleared a White officer in the fatal shooting of an unarmed Black teenager there, Attorney General Eric Holder said on Wednesday.

The report said the St. Louis suburb overwhelmingly arrested and issued traffic citations to Blacks to boost city coffers through fines, used police as a collection agency and created a culture of distrust that exploded in August when Ferguson Officer Darren Wilson fatally shot 18-year-old Michael Brown.

“This investigation found a community that was deeply polarized; a community where deep distrust and hostility often characterized interactions between police and area residents,” Holder told reporters.

Brown’s killing touched off a national debate on race, led to months of street protests and amplified long-standing complaints in Ferguson and across the country of police harassment and mistreatment of minorities. It also prompted Justice Department probes.

“Of course, violence is never justified,” Holder said. “But seen in this context, amid a highly toxic environment, defined by mistrust and resentment, stoked by years of bad feelings, and spurred by illegal and misguided practices, it is not difficult to imagine how a single tragic incident set off the city of Ferguson like a powder keg.”

Holder, who is stepping down soon as attorney general, called for wholesale and immediate change in the way Ferguson operates. The Justice Department has said it will likely seek a court-appointed monitor to implement changes.

The report said city employees made racially disparaging comments in emails, including one where an employee compared President Obama to a chimpanzee.

Ferguson Mayor James Knowles said three police department employees were responsible for the offensive emails. All were put on administrative leave pending a probe and one has since been fired. None of the employees was identified.

Knowles addressed few other specifics in the report but told a news conference, where he read a statement and did not take questions, that the city had launched reforms such as diversity training for police officers and reduced some of the fines levied at municipal court.

“We must do better, not only as a city but as a state and a country,” he said.

The report reviewed the city’s records and found that in a city where Blacks make up about two-thirds of the population, they accounted for 85 percent of the total charges brought by Ferguson police and more than 90 percent of arrests.

Some police would compete to see who could issue the most citations to African-Americans, he said. Often the charges were trumped up, or fictitious.