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"Officers all too frequently plant evidence during searches, rely on excessive force and intimidation as search aids, and proceed with searches even when knowing that the address or identity of the individual or some other pertinent information is simply incorrect," Perez said in September.

Portland, Ore.: In June the DOJ announced the start of an inquiry into allegations of excessive use of force by Portland Police Bureau officers -- use-of-force incidents and officer-involved shootings apparently targeting the city's mentally ill and institutionalized people over the previous 18 months. The Justice Department investigation was expected to take about 18 months to complete.

Denver: In May the Justice Department said that it was at the "threshold stage" of deciding on an investigation of the Denver Police Department and the Denver Sheriff Department for civil rights violations after a decade of arrests involving alleged brutality and questionable fatal shootings, as well as the July 2010 death of Marvin Booker, a black minister who died in the city jail after a struggle with sheriff's deputies. Over that decade, the cases have resulted in $6 million in settlements.

Houston: In February ColorOfChange.org, an organization that advocates on behalf of African Americans, launched an email campaign calling for public outcry and a DOJ investigation into the actions of the Houston Police Department in the 2010 case of Chad Holley, a 15-year-old burglary suspect beaten by four HPD officers while eight other officers looked on.

"It's time to demand real accountability for the Houston Police Department -- and when we do, it'll send a clear message to other departments with a similar problem," the email reads. "What happened to Chad Holley isn't merely an isolated incident -- it's the result of a police culture in Houston (and in police departments across the nation) that places little value on black lives."

A Critical Tool in Reform

The Justice Department can bring any number of resources to bear in these investigations, maybe none as powerful as the consent decree, an agreement between a city and the Justice Department. It is a legally binding contract that often includes the use of federal monitors to assess the progress made in reforming behavior at police departments with a history of civil rights-abuse allegations.