By Lisa Lambert and Carey Gillam WASHINGTON/KANSAS CITY, Mo. (Reuters) - 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. 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. "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.