Protesters shouted in anger while others pleaded for calm Monday night at Philadelphia City Hall after learning of a Missouri grand jury's decision not to indict Police Officer Darren Wilson for the shooting death of Michael Brown.

In anticipation of the announcement, Police Commissioner Charles H. Ramsey said he had officers "standing by" to assist with what he expected to be "peaceful rallies."

Demonstrators began after 8 p.m. to gather at City Hall, where police had already assembled en masse and where ice skaters were enjoying the new rink at Dilworth Park.

After the grand jury's decision was announced, more than 100 demonstrators observed a moment of silence and then began marching through Center City. As the night went on, the number of marchers rose into the hundreds.

"It's just a sad day that our country still sees black men as useless," said one of the marchers, Jay Young, 28, of North Philadelphia.

Chief Inspector Joe Sullivan, who heads the Police Department's civil affairs unit, called Monday night's march "completely peaceful."

"People are angry and they need to vent, and it's their right to do so," he said. "It's our job to make sure we do it safely." He called the protests in Philadelphia "a good night in terms of the First Amendment."

Around midnight, protesters attempted to march onto I-95 from a ramp at the Ben Franklin Bridge. At least two people were arrested.

Clergy and others also filled the pews at Arch Street United Methodist Church, a block from City Hall, and watched the grand jury decision through a live video stream.

At a late-night news conference, Mayor Nutter said, "They have botched this entire tragedy so badly from start to finish."

He added: "I wasn't on the jury. I haven't seen all the evidence, but I am perplexed and astounded that in this case, I did not hear any evidence or, more importantly, justification for why that young man was shot [at] 10 times" after Wilson exited his vehicle and when Brown had no weapon.

Shortly before 9 p.m., a woman outside City Hall took a megaphone and called for a period of silence for Brown. Before that, loud chants - such as "Hey hey, ho, these killer cops have got to go," and "No justice, no peace, no racist police" - had sprung up from the group.

When the silence ended, a man began to rally those in the crowd, asking them to reach out to elected officials or others in their communities able to "repair our community," his voice getting louder as he continued.

"A lot of us are feeling this pain," he said. "And it's being swept up under the rug."

As the clergy and laymen waited for the live feed to deliver the news at Arch Street Methodist, a young man stood up, holding his cellphone, and said news organizations were reporting there would be no indictment.

As soon as the newscast announced that Wilson would not be indicted, the live feed was disconnected and Bishop Dwayne Royster asked for silence.

"Let us now have silence for Michael Brown, because one day he jaywalked and it became a death sentence," Royster said.

The group sat silently for 41/2 minutes and then marched to City Hall, arms raised, chanting, "Hands up, don't shoot!"

Toyia Maxey wiped away a tear before raising her arms again. "More than the one individual, it's what it means for all of us," she said. "For humanity."

By the time the group got to City Hall, the earlier assembled protesters had migrated, so the group delivered a statement for lingering cameras.

"Tonight we stand in pain and thinking about the family of Mike Brown," Royster said. "We are outraged that the image of God in Michael Brown was not respected by the police officer who shot him, and now has been disrespected by the grand jury and the county prosecutor."

"The color of our skin, the clothes we wear, the neighborhoods we live in, even the moods we may be in when we encounter law enforcement, should not negate law enforcement's obligation and responsibility to respect the humanity of every person," he said.

The Rev. Mark Tyler, pastor of Mother Bethel A.M.E. Church, and Royster, founder of Living Water United Church of Christ, went to Ferguson, Mo., in August.

"We were on the ground, we got teargassed, had M-16s pointed at us," Royster said. "We were not treated with respect."

The marchers made their way east on Market Street, then north on Eighth Street through Chinatown toward Police Headquarters, but then returned to City Hall. Sullivan, of the civil affairs unit, said it was the protesters' decision, not that of the police, not to protest outside Police Headquarters.

As the crowd dispersed, Jibri Monk, 22, asked what the protest was about and whether it was over "the boy killed with the toy gun."

Monk, who lives in Northeast Philadelphia, was referring to an incident this weekend in which a black 12-year-old boy with a toy gun in Ohio was fatally shot by a police officer.

"I didn't even know which one they were talking about," Monk said.

Contributing to this article were Inquirer staff writers Claudia Vargas, Aubrey Whelan, and Amy Worden.