New York Mayor Bill de Blasio said the city's police force will undergo significant retraining following the death of Eric Garner, an unarmed black man who was stopped for selling loose cigarettes in New York City and placed in an apparent chokehold by a white police officer.

"The relationship between police and community has to change. The way we go about policing has to change," de Blasio said at a news conference on Thursday

"​It has to change in this city. It has to change in this country. I am fundamentally conviced it will change."

De Blasio pledged that this new training would change the future of the city. He said it would include focusing on changing how officers talk with and listen to residents of the city, deescalating situations, getting officers to wait for back up and using less force whenever possible.

Earliler, U.S. Attorney General Eric Holder says federal prosecutors are launching their own inquiry into Garner, an unarmed black man who was stopped for selling loose cigarettes in New York City and placed in an apparent chokehold by a white police officer.

The announcement about a separate civil rights investigation came after a grand jury on Wednesday cleared officer Daniel Pantaleo in the July 17 incident. The ruling triggered protests in the streets by hundreds of New Yorkers who likened the case to the deadly police shooting in Ferguson, Mo.

Staten Island District Attorney Daniel Donovan said the grand jury found "no reasonable cause" to bring charges, but unlike the chief prosecutor in the Ferguson case, he gave no details on how the panel arrived at its decision. The grand jury could have considered a range of charges, from reckless endangerment to murder.

Protesters gathered in Times Square and converged on the heavily secured area around the annual Rockefeller Center Christmas tree lighting with a combination of professional-looking signs and hand-scrawled placards reading, "Black lives matter" and "Fellow white people, wake up." And in the Staten Island neighbourhood where Garner died, people reacted with angry disbelief and chanted, "I can't breathe!" and "Hands up β€” don't choke!"

USA-NEW YORK/CHOKEHOLD

Protesters, demanding justice for the death of Eric Garner, shout at police at a roadblock in midtown Manhattan in December. (Adrees Latif/Reuters)

Garner's mother, Gwen Carr, said the grand jury decision "just tore me up."

"I couldn't see how a grand jury could vote and say there was no probable cause," she said. "What were they looking at? Were they looking at the same video the rest of the world was looking at?"

In his first public comments, Pantaleo said he prays for Garner's family and hopes they accept his condolences.

"I became a police officer to help people and to protect those who can't protect themselves," he said in the statement. "It is never my intention to harm anyone, and I feel very bad about the death of Mr. Garner."

Police union officials and Pantaleo's lawyer argued that the officer used a takedown move taught by the police department, not a banned manoeuvre, because Garner was resisting arrest. They said his poor health was the main reason he died.

A video shot by an onlooker and widely viewed on the internet showed the 43-year-old Garner telling a group of police officers to leave him alone as they tried to arrest him. Pantaleo responded by wrapping his arm around Garner's neck in what appeared to be a chokehold, which is banned under New York Police Department policy.

The heavyset Garner, who had asthma, was heard repeatedly gasping, "I can't breathe!"

Experts said that without knowing how prosecutors presented the case, it's difficult to theorize how the grand jury reached its decision. To find Pantaleo criminally negligent, the panel would have had to determine he knew there was a "substantial risk" that Garner would have died.

Police Chokehold Death

Eric Garner, right, shown posing with his children during a family outing. The 43-year-old died after an officer wrapped his arm around Garner's neck in a chokehold, which is banned under NYPD policy.

Critics of the outcome in Ferguson β€” where a grand jury refused last week to indict a white police officer who shot unarmed black 18-year-old Michael Brown β€” complained that prosecutors there allowed the officer to give a self-serving account without challenging inconsistencies.

The Garner video "speaks for itself," said Jeffrey Fagan, a professor at Columbia Law School. "It appears to show negligence. But if we learned anything from the Brown case, it's the power of prosecutors to construct and manage a narrative in a way that can shape the outcome."

Grand jury investigation details could be released

While details on the grand jurors were not disclosed, Staten Island is the most politically conservative of the city's five boroughs and home to many police and firefighters. The district attorney said he will seek to have information on the investigation released.

The medical examiner ruled Garner's death a homicide and found that a chokehold contributed to it. A forensic pathologist hired by Garner's family agreed with those findings, saying there was hemorrhaging on Garner's neck indicative of neck compressions.

Pantaleo was stripped of his gun and badge and will remain on desk duty pending an internal police investigation that could result in administrative charges.

As the grand jury decision drew near, police officials met with community leaders on Staten Island to head off the kind of violence seen in Ferguson, where arson and looting resulted in more than 100 arrests and the destruction of 12 commercial buildings by fire.

With files from CBC News