U.S. Attorney General Eric Holder announced Wednesday night a federal civil rights investigation would be opened in the case of Eric Garner, hours after a Staten Island grand jury declined to indict the NYPD officer who held him in an apparent chokehold that led to his death.

The announcement came as hundreds of protesters swarmed into Times Square and other major New York City landmarks, including Rockefeller Center, where the annual tree lighting ceremony is taking place. There were at least several arrests. An NYPD spokesman declined to say how many protesters were arrested until all the demonstrations are over Wednesday night.

The grand jury deliberated earlier Wednesday and decided no homicide charges were warranted against Officer Daniel Pantaleo. Garner, 43, died July 17 after Pantaleo held him in an apparent chokehold during a confrontation with cops while being arrested on suspicion of selling loose, untaxed cigarettes.

"The grand jury found no reasonable cause to vote an indictment," said Richmond County Attorney Daniel M. Donovan, in a statement.

Mayor Bill de Blasio issued a statement calling the decision by the grand jury "one that many in our city did not want."

"Yet New York City owns a proud and powerful tradition of expressing ourselves through non-violent protest," he said. "We trust that those unhappy with today’s grand jury decision will make their views known in the same peaceful, constructive way."

After learning of the decision, Pantaleo, 29, issued a statement through the Patrolmen's Benevolent Association: "I became a police officer to help people and to protect those who can't protect themselves. It is never my intention to harm anyone, and I feel very bad about the death of Mr. Garner. My family and I include him and his family in our prayers and I hope that they will accept my personal condolences for their loss."

Ben Carr, Garner's stepfather, said the decision is "just like a knife stabbing my heart."

Grand jury proceedings are secret, but Donovan said his office conducted a four-month investigation, including 38 interviews and experts in forensic pathology and the training of police officers. The evidence gathered was then presented to the 23-member grand jury.

He said he was seeking authorization to release publicly information from the grand jury proceedings.

The medical examiner ruled Garner's death on July 17 a homicide from compression of the neck as well as "compression of chest and prone positioning" while being restrained by the police. The medical examiner's office also said that the 350-lb man's asthma, obesity and heart disease were contributing factors.

An attorney for Garner's family said that relatives plan to press federal authorities to launch an investigation. The family filed a $75 million notice of claim with the city in October, the first step in a lawsuit.

Pantaleo is not out of woods since he now faces the prospect of command discipline and an Internal Affairs Bureau probe, said police officials. Police investigators will be closely looking at whether Pantaleo used excessive force, including a chokehold that is against NYPD protocol, said one law enforcement official. A bystander video of the incident depicted Pantaleo grabbing Garner and taking him down with what appeared to be a chokehold move.

Wednesday's decision comes days after a grand jury in Ferguson, Missouri, also declined to indict a white police officer who fatally shot a black teenager, Michael Brown, sparking days of sometimes violent protests. The nationwide backlash following the Missouri grand jury's decision forced the officer, Darren Wilson, to resign from the police department.

New York City officials had been preparing for likely protests in case the grand jury declined to indict the officer. Protesters were already planning marches, possibly including to the federal prosecutors' office in Brooklyn. Police Commissioner William Bratton has met with local officials on Staten Island to notify them to expect an increased police presence.

Garner's family has called for a peaceful response to the grand jury's decision, whatever the outcome. "We don't want violence," said Gwen Carr, Garner's mother, late last week. "We don't want them burning up the place. We live here."

Local elected leaders and civil rights groups quickly lashed out at the decision by the grand jury.

"This was a terribly disappointing outcome and is not reflective of the events that led to Eric Garner's death," City Council Speaker Melissa Mark-Viverito said in a statement, while urging the U.S. Department of Justice to launch an investigation.

Public Advocate Letitia James said she was "saddened" by the grand jury's decision. "The fact that there will be no public trial is shocking and unconscionable," she said in a statement. She said she was calling on the governor and attorney general to create a special prosecutor to investigate alleged police misconduct cases.

Donna Lieberman, the executive director of the New York Civil Liberties Union, urged the NYPD to hold the officers involved in Garner's death "accountable" and to "ensure that this is the last tragedy of its kind."

Earlier this year, Bratton committed to retaining all officers in the department, promising a "top-to-bottom" review of all police training procedures following Garner's death. The new training will focus on discretion, how to de-escalate tense situations as well as conflict resolution and tactics in a three-day yearly course, he said at the time.

In Brooklyn a pair of NYPD officers were indicted last month for allegedly assaulting a 16-year-old boy in August, knocking his teeth out, in an incident caught on video.

— With Alison Fox