A New York City grand jury decision not to charge a white police officer who killed an unarmed black man with a chokehold has sparked outrage and protests.
The US Justice Department has said it would investigate the incident, which happened on Staten Island, New York City's smallest borough.
Eric Garner, a 43-year-old father-of-six, was illegally selling cigarettes on 17 July when police officers tackled him and put him in a chokehold.
Police said he had been resisting arrest.
The city's medical examiner ruled the death a homicide.
The incident has fuelled debate about how US police use force, particularly against minorities.
Last week, a grand jury in Missouri decided not to indict a white police officer in another racially charged killing of a black man.
The decision in that case sparked a spasm of violence in Ferguson, Missouri, with businesses burned and looted.
The Justice Department is investigating whether Michael Brown's civil rights were violated through excessive force.
Today, about two dozen demonstrators lay down in Grand Central Terminal's main hall in Midtown Manhattan in a silent protest as the evening rush hour began.
In Times Square, about 200 people gathered, chanting "No indictment is denial. We want a public trial."
On Staten Island, some demonstrators defiantly crushed cigarettes in front of reporters and passersby - a reference to the reason that police gave for approaching Mr Garner in the first place.
US President Barack Obama, while not directly commenting on the case, said the grand jury decision spoke to "the concern on the part of too many minority communities that law enforcement is not working with them and dealing with them in a fair way.
"We are not going to let up until we see a strengthening of trust and strengthening of accountability that exists between our communities and our law enforcement," he said.
New York Mayor Bill de Blasio, speaking at a press conference on Staten Island, said he had spoken to US Attorney General Eric Holder and the US attorney for the Eastern District of New York, Loretta Lynch.
"They made clear that the investigation initiated by the US attorney would now move forward and would be done expeditiously, and would be done with a clear sense of independence and that it would be a thorough investigation," Mr de Blasio said.
The district attorney for Staten Island, Daniel Donovan, announced the grand jury's decision not to indict the police officer, Daniel Pantaleo, who placed Mr Garner in a chokehold.
"It is never my intention to harm anyone and I feel very bad about the death of Mr Garner," Mr Pantaleo said in a statement released by the Patrolmen's Benevolent Association union.
Benjamin Carr, the stepfather of Mr Garner, said he was distraught over the verdict.
"The justice system didn't do what it was supposed to do," he said.
