By Michael Doyle

As the Justice Department pursues new cases involving the deaths of black suspects, a recent North Carolina courtroom clash shows what can happen when the federal government becomes entangled with local policing. It can get uglier than a mug shot.

But federal oversight can also promote progress, albeit with rocky starts. In cities such as Seattle, official monitors are applauding certain police department changes compelled by agreements reached with the Justice Department.

How federal intervention in local law enforcement works out appears to matter now more than ever.

The Justice Department has launched a civil rights investigation into the shooting death by police of Michael Brown, an 18-year-old black teenager in Ferguson, Mo. Attorney General Eric Holder pledged a similar inquiry into the death of 43-year old Eric Garner of New York, who died after being placed in a chokehold by a police officer.

Both Brown and Garner were unarmed. Both police officers involved were white. And in both cases, grand juries declined to indict the officers, triggering street protests in several cities and a national debate over race and police violence.

A related civil rights investigation into the Ferguson Police Department might lead to a consent decree with the Justice Department _ a court-enforced and publicly monitored agreement that spells out specific steps to be taken.

"They have been proven to be effective as a means of reform for troubled departments that have been incapable of reforming themselves," Samuel Walker, an emeritus professor of criminal justice at the University of Nebraska Omaha, said of consent agreements in an interview.

The Obama administration's Justice Department has opened more than 20 investigations of local law enforcement agencies, which Holder noted Thursday is "more than twice as many as were opened in the previous five fiscal years."

These are investigations of institutions, and they're separate from the civil rights investigations into individual officers who kill civilians.

Sometimes federal investigators have given local agencies clean bills of health. In the past five years, inquiries by the Justice Department's Special Litigation Section, part of the Civil Rights Division, found no pattern or practice of unconstitutional violations in five local law enforcement agencies that had been under scrutiny.

In September 2012, for instance, federal officials closed an investigation of the Escambia County Sheriff's Office, in westernmost Florida, despite lingering problems cited by the Justice Department, such as what it called excessive use of stun guns. In May 2011, the Justice Department amicably closed a four-year investigation of the Austin Police Department in Texas.

Sometimes, local officials resist the federal oversight.

After a two-year investigation, Justice officials concluded in 2012 that the Alamance County Sheriff's Office in central North Carolina had engaged in discriminatory policing practices against Latinos. Sheriff Terry Johnson refused to negotiate a settlement agreement, and the Justice Department sued.

A nine-day trial ensued last August in the federal courthouse in Winston-Salem. More recently both sides have presented U.S. District Judge Thomas Schroeder with their final post-trial arguments.

"Before an operation at the predominantly Latino Rocky Top mobile home park, Sheriff Johnson ordered two Gang Unit officers to 'go get me some Mexicans,' " the Justice Department recounts in its 149-page post-trial brief.

Over a five-year period, other testimony showed, Latinos made up 36.8 percent of all checkpoint stops, despite composing only 8.6 percent of the driving-age population in Alamance County. But in their own 131-page post-trial brief, the Raleigh-based attorneys who are defending the sheriff deny allegations of discrimination.

"The government asserted that (the sheriff department's) roundups were discriminatorily based," the defense attorney noted. "However, the uncontroverted evidence reveals that upwards of 90 percent of drug traffickers in Alamance County are not only Hispanic, but from Mexico."