On July 17, Mr Eric Garner, 43, a black father of six and grandfather of two, was stopped by the police on a street in New York's Staten Island. White police officer Daniel Pantaleo, in an attempt to place him under arrest, placed Mr Garner in a chokehold. Mr Garner died after the incident.

On Dec 3, a grand jury decided that Officer Pantaleo should not face criminal charges in the death of Mr Garner. The decision sparked protests from Staten Island to Times Square in Manhattan.

Here's what you should know about the case:

What happened?

Mr Garner was questioned by the police on a street in Staten Island at about 5pm on July 17, suspected of selling illegal, untaxed cigarettes. As they attempted to arrest him, Mr Garner resisted, and Officer Pantaleo came from behind and put the suspect under a chokehold, as the officer and at least four other colleagues wrestled the 159kg Mr Garner to the ground. The suspect's head also appeared to have been slammed onto the sidewalk.

Much of the confrontation was recorded on video by passers-by. Graphic cellphone footage showed Mr Garner, who has asthma, complaining "I can't breathe, I can't breathe" after being bundled onto the ground by the officers. Officer Pantaleo can be seen standing behind Garner and wrapping an arm around his neck.

Mr Garner's body soon became limp and the officers called paramedics to the scene.

What did the autopsy show?

An autopsy by the city's medical examiner called his death a homicide resulting from the chokehold and the compression of his chest by police officers.

What did the police officer say about the incident?

In his testimony in front of the grand jury, Officer Pantaleo, who has been a New York City Police Department officer for eight years, said he never meant any harm to Mr Garner, and the chokehold that he had used - a move banned by the Police Department, but not explicitly against state law - was part of a manoeuvre taught to him at the Police Academy where he puts his arms around a suspect to "tip the person so they lose their balance and go to the ground", as seen in wrestling matches.

The officer also acknowledged that he had heard Mr Garner saying he could not breathe, and tried to get off him as quickly as he could.

However, videos of the incident appear to show that Officer Pantaleo's arm around Mr Garner's neck held firm and did not move even after the suspect toppled to the ground, seemingly contradicting the above claim.

Officer Pantaleo told the jurors he continued to hold on to Mr Garner as he struggled to regain his balance and wanted to make sure that Mr Garner was not injured by the other officers rushing in.

Why are there so many protests?

The protests in America's largest city of New York, which have paralysed its streets since Wednesday, is a response to the racially tinged nature of the killing, and perceived police brutality against black people in the United States.

They have been joined by protesters in Washington, Boston, Chicago and San Francisco, among other cities across the US.

America has been inflamed in recent months over a series of incidents where black people have been killed by the police, including the case of unarmed black teen Michael Brown, where a grand jury failed to bring charges against a white police officer who shot him dead in August.

The police in Cleveland last month also shot dead a 12-year-old black boy Tamir Rice, who was brandishing a toy gun at a park. The Justice Department said a nearly two-year investigation into the Cleveland police department had found a pattern of "unreasonable and unnecessary use of force" that resulted in dangerous and reckless behaviour by officers.

And in the latest incident on Wednesday, 34-year-old black man Rumain Brisbon was shot dead by the police outside a convenience store in Arizona. Mr Brisbon was shot after the police thought he was reaching into his pocket for a gun. It was later found that he had only pills in his pocket.

The protests over the grand jury decision on Mr Garner's death is the latest controversy to fan the flames.

They also come after a recent series of violent protests in Ferguson, Missouri and other cities across the US last month, sparked by the Michael Brown case.

The cases, especially the the New York and Missouri one, have reignited debate over a US law enforcement system widely perceived to unfairly target and African Americans and other minorities.

Even some conservatives who stood by the police in Ferguson have condemned the police action on Staten Island, and slammed the grand jury decision not to charge Officer Pantaleo.

What actions are going to be taken?

Whether any major policy changes will come from these episodes remains to be seen. The US Justice Department is currently investigating the cases, with the probe in New York led by attorney Loretta Lynch, who is President Barack Obama's nominee to replace Attorney-General Eric Holder.

The Justice Department has already announced that it would open a civil rights investigation into Mr Garner's death, raising hopes that the federal government will succeed in obtaining an indictment where Staten Island prosecutors failed.

Mr Obama has also set up a task force on policing, which aims to promote the use of body cameras on officers and other measures that would encourage more trust between law enforcement agencies and the communities they serve.

He has also discussed with New York Mayor Bill de Blasio how more can be done to repair relations between the police and the citizens, and strengthen trust and bonds.

Sources: Bloomberg, Agence France-Presse, Reuters, New York Times, Washington Post, New York Daily News