NEW YORK - From the White House to the streets of some of America's biggest cities, the New York chokehold case converged with the Ferguson shooting and investigations out of South Carolina and Cleveland to stir a national conversation Thursday about racial justice and police use of force.

A day after a grand jury cleared a white New York City officer in the death of a black man, civil-rights leaders pinned their hopes on a promised federal investigation. Demonstrators protested for a second night in New York and turned out in such cities as Denver, Detroit and Minneapolis. And politicians and others talked about the need for better police training, body cameras and changes in the grand jury process to restore faith in the legal system.

"A whole generation of officers will be trained in a new way," New York Mayor Bill de Blasio vowed. He and his police commissioner outlined previously announced plans to teach officers how to communicate better with people on the street.

President Obama weighed in, saying one of the chief issues at stake is "making sure that people have confidence that police and law enforcement and prosecutors are serving everybody equally."

At a news conference in New York after a night of protests led to 83 arrests, the Rev. Al Sharpton called the state-level grand jury system "broken" when it comes to police brutality cases and urged federal authorities to fix it.

"The federal government must do in the 21st century what it did in the mid-20th century," he said. "Federal intervention must come now and protect people from state grand juries."

Still, federal civil-rights cases against police officers are exceedingly rare.

In the last two decades, only a few such cases have reached trial in New York - most notably the one involving Abner Louima, who was sodomized with a broom handle in a police station in 1997. Several other high-profile cases didn't come together.

That's largely because federal prosecutors must meet a high standard of proof in showing that police deliberately deprived victims of their civil rights through excessive force, said Alan Vinegrad, who as a federal prosecutor handled the Louima case.

Federal intervention "doesn't happen often, and it shouldn't happen often," said James Jacobs, a constitutional law professor at New York University Law School. "They should only step in when the local prosecution was a sham."

Activists have claimed that the grand jury investigation of Garner's death was indeed a sham. An amateur video showed Officer Daniel Pantaleo putting Garner in an apparent chokehold, and the medical examiner said the maneuver contributed to the death.

But Pantaleo's attorney, Stuart London, expressed confidence on Thursday that his client won't face federal prosecution.

"There's very specific guidelines that are not met in this case," London said. "This is a regular street encounter. It doesn't fall into the parameters."

Acting at the Staten Island district attorney's request, a judge released a few details Thursday from the grand jury proceedings - among other things, it watched four videos and heard from 50 witnesses, 22 of them civilians. District Attorney Daniel Donovan didn't ask for testimony, transcripts, or exhibits to be made public.

But London offered some details on Thursday, saying the officer's testimony focused on "his remorse and the fact that he never meant to harm Mr. Garner that day."