Marchers in Washington, New York, Boston Protest Police Killings

Organizers said the marches were among the largest in the recent wave of protests against the killings of black males by officers in Ferguson, Missouri; New York; Cleveland; and elsewhere. The protests were peaceful, although police in Boston said they arrested more than 20 people who tried to block a highway.

Decisions by grand juries to return no indictments against the officers involved in the deaths of Michael Brown in Missouri and Eric Garner in New York have put police treatment of minorities back on the national agenda.

"We're going to keep the light on Mike Brown ... on all of the victims. The only way you make roaches run is to keep the light on," said civil rights leader the Rev. Al Sharpton, whose National Action Network organized the Washington rally.

Protesters from around the country gathered at Freedom Plaza, a few blocks from the White House, then marched down Pennsylvania Avenue to rally near the white-domed U.S. Capitol.

Marchers, who included many parents with children, chanted "No justice, no peace, no racist police" and "Hands up, don't shoot." Protesters carried signs that said "All men are created equal" and "Black lives matter."

Sharpton urged Congress to pass legislation that would allow federal prosecutors to take over cases involving police violence.

The Washington protest included relatives of Eric Garner and Akai Gurley, who were killed by New York police; Trayvon Martin, slain by a Florida neighborhood watchman in 2012; Brown; and others.

"Wow, what a sea of people," said Brown's mother, Lesley McSpadden. "If they don't see this and make a change, I don't know what we're going to do."

In Missouri, a prosecutor on Saturday made public documents related to the probe into Brown's killing, saying his office had inadvertently held them back.

After the march in Washington, protesters gathered in a one-block section of Pennsylvania Avenue and nearby public space, although organizers estimated the crowd at 40,000 to 50,000 people. A police spokesman declined to provide a crowd estimate, citing department policy, and said there had been no arrests.

In Boston, police arrested at least 23 people near Interstate 93 as demonstrators attempted to block the highway, the Massachusetts State Police said in a statement. All were charged with disorderly conduct.

The New York march drew a mostly young, ethnically diverse crowd that was loud and peaceful as it headed north up Manhattan's Fifth Avenue from Washington Square Park. The march was to circle back and end at the city's police headquarters.

Protesters chanted "How do you spell racist? NYPD" and some taunted police guarding the march route.

"The culture in America is embedded in slavery, in the courts and the politics, and the culture has to change," said marcher Kayode Leonard, 33, from Manhattan.

Observers estimated that more than 10,000 protesters marched in New York. Police gave no estimate of crowd size and reported no arrests.