 -- Attorney General Eric Holder announced tonight that the Justice Department will launch a civil rights investigation into the death of Eric Garner, the unarmed black man who died after being placed in a choke hold by a white New York City police officer during an arrest last summer.

The announcement came just hours after a Staten Island grand jury declined to indict officers involved in Garner’s arrest. Garner died July 17 after being placed in a chokehold by Officer David Pantaleo. The incident was caught on tape, and shows that Garner was unarmed and posing no apparent threat to the half-dozen officers who surrounded him.

After he was taken down in the chokehold by Pantaleo, other officers held him down. Garner can be heard on tape saying, “I can’t breathe.”

Holder said the department will conduct an “independent, thorough, fair and expeditious investigation. He noted that many have seen the video of the incident, and that, “all lives must be valued, all lives.”

He said the federal investigation would review all aspects of the case. “We must seek to heal the breakdown in trust that we have seen, “ he said.

The Staten Island decision follows a similar finding by a grand jury in Missouri in the case of Michael Brown, the unarmed, black teen who was shot in a confrontation with Ferguson Police Officer Darren Wilson.

The Missouri grand jury decision sparked some violent demonstrations in Ferguson, and days of demonstrations in dozens of cities around the country. New York authorities have prepped a similar reaction following the decision in Staten Island.

The attorney general pointed out these incidents “have tested the sense of trust that must exist between law enforcement and the communities they are charged to serve and protect.” He added, “This is not a New York issue or a Ferguson issue alone. Those who have protested peacefully across our great nation following the grand jury’s decision in Ferguson have made that clear.”

Tonight, as crowds of protesters gathered in New York, Washington, D.C., and other cities, the attorney general sent them a message.

“I urge all those inclined to demonstrate tonight and in the days ahead to remain peaceful in their demonstrations, and not to engage in activities that deflect our attention from the very serious matters our nation must confront."

Now, the Justice Department finds itself at the center of cases involving race that have captured the attention of a divided nation.

ABC's Meghan Keneally and Josh Margolin contributed reporting.