Lawyers for the family of Michael Brown have criticised the grand jury process that led to a decision not to indict the white police officer who shot and killed the black teenager in Ferguson, Missouri in August, the BBC reports.
The jury's ruling prompted a night of rioting and protests in Ferguson, while thousands protested in other US cities, from Los Angeles to New York.
One of the family's lawyers, Benjamin Crump, said the process was not properly carried out.
“We could foresee what the outcome was going to be and that's exactly what occurred last night, but it is awfully troubling when you look at what was released and you hear about the police officer who shot Michael Brown Jnr,” he said.
“And you have to scratch your head, kind of like we all did, to say, when is the prosecutor going to cross-examine the killer of an unarmed person?”
President Barack Obama joined the teenager's family in appealing for calm, urging Americans to accept the decision was “the grand jury’s to make”.
Authorities said more than 80 people were arrested amid chaos in several areas of St Louis overnight. Sixty-one of those arrests were in Ferguson - a predominantly black community patrolled by a mainly white police force - with charges including burglary and trespassing.
As protesters charged barricades, hurling glass bottles, police responded with smoke and tear gas.