But an analysis by The Associated Press found that the racial gap between black police officers and the communities where they work has narrowed over the last generation, particularly in departments that once were the least diverse.
A much larger disparity, however, is now seen in the low number of Hispanic officers in police departments. In Waco, Texas, for example, the community is more than 30 percent Hispanic, but the police department of 231 full-time sworn officers has only 27 Hispanics.
Across the U.S., there are police departments that still look like Ferguson, Missouri, a largely white police force protecting a mostly black community.
After rioting followed the shooting of Michael Brown there, Attorney General Holder noted the lack of black police on the city's payroll. “Police forces should reflect the diversity of the communities they serve,” Holder said.
Holder on Thursday announced a Justice Department investigation into the practices of the city's police department. Holder said he and his department had heard numerous concerns from people in Ferguson about police practices, a history of “deep mistrust” and a lack of diversity on the police force.
But the situation in Ferguson is less common than it was 20 years ago. In most cases now, underrepresented minority populations in police departments are found in places such as Anaheim, California, West Valley City, Utah, and Providence, Rhode Island, where there are large Hispanic populations, yet few Hispanic officers.
Less common today are the circumstances in cities such as Ferguson, Chester, Pennsylvania, and Maple Heights, Ohio, where most of the sworn officers are white and are protecting largely black communities.
In Anaheim, for instance, where the police department is among the least racially balanced in the nation, the police killings of two Latino men in 2012 set off weeks of angry protests. While more than half the community is Hispanic, only 23 percent of the sworn police officers are.
“There's a huge gap between community and police,” said Theresa Smith, a member of the Anaheim Community Coalition, which aims to improve police oversight. Police shot and killed Smith's son in 2009. “You can't bridge that gap if people don't trust you.”
The AP compared Census Bureau data about a community's racial and ethnic makeup with staffing surveys by the Justice Department for more than 1,400 police departments from 1987 and 2007, the most recent year for which the data are available. The AP then analyzed how different a department's racial makeup was from the population it served.
The AP found that since 1987, black representation on police forces has improved, such as in New Orleans and in East Orange and Plainfield, New Jersey.
At least 49 departments had a majority Hispanic population, yet more than half of the police department was white. That's nearly five times as many departments than in 1987, when the largest disparities disproportionately involved black police officers and residents.
Efforts to improve relationships between police departments and communities date to the 1950s and 1960s, when some departments started creating community relations units.
Among the most balanced police departments in diverse cities are in Miami Beach, Florida, Oak Park Village, Illinois, Pasadena City, California, Bexar County, Texas, Cambridge, Massachusetts, New Orleans, Seattle and Washington, D.C.
One benefit of diversity is to avoid the perception of discrimination, said Anthony Chapa, executive director of the Hispanic American Police Command Officer Association.
But a diversified police force does not solve all the problems.
The AP found that even in cities where police departments reflect the communities they protect, there still are issues with racial discrimination. Police may not be able to hire their way out of problems.
New Orleans, for example, is among the most racially balanced departments in the country. Yet in 2011, the Justice Department found that it discriminated against African-Americans. There are similar concerns in the Hispanic community.
The executive director of Puentes New Orleans, Carolina Hernandez, said her group has been working with local police to bridge the divide between officers and the Latino community. “If you're here to protect and serve,” she said, “it's hard to accomplish that when the community automatically doesn't trust you.”
The U.S. government recognized the importance of recruiting more minority police officers as early as 1968, with that recommendation from the National Advisory Commission on Civil Disorders, convened by President Lyndon Johnson after deadly riots in a series of cities the previous year. But it would be years before police departments made real efforts. Some departments still struggle with it today.
“It is one of the challenges that I inherited,” said Adrian Garcia, the sheriff in Harris County, Texas. The first Hispanic sheriff of the sprawling county that includes Houston, Garcia said his department is not representative of the community. But he's trying to change that.
“I call myself the chief recruiter,” Garcia said. “I have to talk to the community and let them know what we want their sons and daughters to serve the community.”
Garcia said he does not think a police department that does not look like the community it protects is more prone to discrimination than more racially diverse departments.
“But it leaves that perception,” Garcia said. “As long as the community can point and say, ‘There's no one that looks like me, and as a result, I feel like I was treated unjustly,' it opens up the argument that maybe the policies are shortsighted in how you work with a diverse community.”
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