WASHINGTON — Ferguson, Mo., is a third white, but the crime statistics compiled in the city over the past two years seemed to suggest that only black people were breaking the law. They accounted for 85 percent of traffic stops, 90 percent of tickets and 93 percent of arrests. In cases like jaywalking, which often hinge on police discretion, blacks accounted for 95 percent of all arrests.

The racial disparity in those statistics was so stark that the Justice Department has concluded in a report scheduled for release on Wednesday that there was only one explanation: The Ferguson Police Department was routinely violating the constitutional rights of its black residents.

The report, based on a six-month investigation, provides a glimpse into the roots of the racial tensions that boiled over in Ferguson last summer after a black teenager, Michael Brown, was fatally shot by a white police officer, making it a worldwide flash point in the debate over race and policing in America. It describes a city where the police used force almost exclusively on blacks and regularly stopped people without probable cause. Racial bias is so ingrained, the report said, that Ferguson officials circulated racist jokes on their government email accounts.

In a November 2008 email, a city official said Barack Obama would not be president long because “what black man holds a steady job for four years?” Another email included a cartoon depicting African-Americans as monkeys. A third described black women having abortions as a way to curb crime.