Protesters stare at a line of police officers and National Guard soldiers during a protest to demand justice for the killing of 18-year-old Michael Brown, outside the Ferguson Police Department in Ferguson, Missouri in this file photo taken November 28, 2014. [Photo/Agencies]

Jackson did not respond to a request for comment.

One email sent by a Ferguson police or municipal court official joked in 2008 that Obama would not stay in office long because, "What black man holds a steady job for four years?"

Ferguson Committeewoman Patricia Bynes said she was outraged by that and other racially tinged emails found in the investigation.

"The fact that police officers and municipal court officials are using their public emails to tell racial jokes, that just reeks of arrogance and ignorance," said Bynes. "It's astounding. They think they are untouchable. The taxpayers have been paying for that racial bias."

The official said that in Ferguson's court system, African-Americans were less likely to have their cases dismissed by a municipal judge and made up 95 percent of people held longer than two days in the Ferguson jail.

The Ferguson Municipal Court, which Attorney General Eric Holder has previously criticized for unfairly penalizing the city's poor, issued the majority of its warrants for minor violations such as parking, traffic and housing code violations.