WASHINGTON (AFP) - After a Missouri grand jury did not charge a white police officer with any crime in the shooting death of black teen Michael Brown, his family and supporters are pinning their hopes on federal charges.
The Justice Department quickly opened its own investigations in the wake of the Aug 9 shooting of Michael Brown, who was unarmed, by Officer Darren Wilson in the St Louis suburb of Ferguson.
One arm of the probe is to determine whether Wilson violated Brown's civil rights.
The second is looking at whether the Ferguson police department as a whole engages in racial profiling or employs excessive force.
After protesters looted Ferguson businesses and set fire to buildings on Monday, Attorney General Eric Holder tried to reassure residents disappointed in the legal system.
"The department's investigations will continue to be thorough," Holder said. "They will continue to be independent and they remain ongoing."
He said he hoped the probes could "restore trust" between law enforcement and members of the community.
In August, after Brown was shot dead and Ferguson was convulsed by violence, Holder quickly visited the town and said he understood how black residents were wary of the mainly white police force.
"I understand that mistrust. I am the attorney general of the United States. But I am also a black man," he said.
After the grand jury decision was made public, President Barack Obama said that the situation in Ferguson "speaks to the broader challenges that we still face as a nation."
"A deep distrust exists between law enforcement and communities of colour," said Obama, America's first black president.
Nevertheless, more than three months after Brown's death, the Obama administration has announced no charges and leaks to the US media suggest federal cases may not be forthcoming.
St Louis County prosecutor Robert McCulloch said federal and local authorities had shared all information in their parallel investigations and that the evidence had not been sufficient to indict Wilson.
Holder, who has been seen as a champion of civil rights during his tenure as the nation's first black attorney general, is due to leave office soon.
- Not much room for error -
After the Brown family said it was "profoundly disappointed" in the grand jury's decision, rights campaigners called on federal authorities to act.
"We may have lost one round, but the fight is not over," civil rights firebrand Al Sharpton told reporters on Tuesday, calling for a nationwide day of protest on Saturday.
The PICO network of faith-based community organisations said the failure to charge Wilson was "a reflection of a biased judicial system that dehumanizes and devalues the lives of black youth." Sherrilyn Ifill, the president and director-counsel of the NAACP Legal Defence and Educational Fund, meanwhile urged federal authorities to "move forward expeditiously" with their investigations.
"It's time for the DOJ to finally address the problem of racial profiling by law enforcement agencies - both in policy and practice," railed Anthony Romero of the American Civil Liberties Union.
But for a Justice Department case to move forward, the bar is high.
"The fact that the officer was white and Mr Brown was African American is not conclusive of anything," said Paul Millus, a litigator with the law firm of Meyer, Suozzi, English and Klein.
Millus said that unless there is evidence that Wilson's actions were motivated by racial prejudice it is "highly unlikely" that any prosecution on US civil rights grounds would go ahead.