Members of the National Association for the Advancement of Colored People and other demonstrators march in Ferguson, Missouri, on November 29, 2014
Ferguson (United States) (AFP) - US activists launched a week-long march in Missouri to demand sweeping police reforms as the white officer who shot dead an unarmed black teen in Ferguson resigned.
The officer, 28-year-old Darren Wilson, has left the force, citing safety concerns, according to a letter published by local media Saturday.
A grand jury's decision last Monday not to charge Wilson in connection with the August 9 shooting death of 18-year-old Michael Brown touched off days of sporadic violence in Ferguson, a suburb of St Louis.
On Saturday, a core group of about 100 marchers, many from other states, set out on a 120-mile (192-kilometer) "Journey for Justice," heading from the St Louis suburb of Ferguson to the Missouri state capital Jefferson City.
The marchers, organized by the National Association for the Advancement of Colored People (NAACP), are demanding the sacking of the Ferguson police chief, nationwide police reforms and an end to racial profiling.
"We will fight until hell freezes over, and then we will fight on the ice," NAACP president Cornell William Brooks told supporters at Washington Metropolitan A.M.E. Zion Church before setting out.
The march is the latest in a series of protests that have taken place across the United States in the wake of the explosive grand jury decision not to indict Wilson.
Wilson wrote in his letter "it is my hope that my resignation will allow the community to heal."
The grand jury decision revived long-standing questions about how police, especially white officers, interact with African Americans -- questions raised again after last week's shooting in Cleveland of 12-year-old Tamir Rice.
"What we're endeavoring to do here is seek justice for a grieving family as well as systemic, fundamental reform in terms of policing for an outraged community," Brooks told reporters.
"When you have a 12-year-old child who is killed with a toy gun in his hand, there is something fundamentally wrong," Brooks said.
- Fighting from the start -
But when the group of older activists arrived at the memorial of flowers and soft toys where Brown was killed, some protesters who have been out since August wondered why they had shown up only now.
"I've been out here fighting the fight from the beginning," said Markese Mull, celebrating his 40th birthday and a member of the local Peacekeepers group pushing for a better future and working to stop violence at demonstrations.
Eugene Gillis, a trumpeter who plays at nightly protests, said young protesters feel alienated and reject the older generation of activists molded by slain civil rights leader Martin Luther King, Jr.
"Most of these young people say these people are out here for photo ops and that's what aggravates the issue," Gillis told AFP.
Brooks, dressed in neat jeans and a sweater, prayed and fell to his knees in reflection at Brown's memorial while surrounded by a media scrum.
Mobbed by TV cameras, he then led the march in one direction before turning around and heading back the opposite way, marching into West Florissant Avenue, where some of the worst looting took place.
The marchers, including young children, were tailed by two buses in case they got tired, and a convoy of cars. The group told AFP they would march around 10 miles on Saturday, before returning to the church to sleep.
Outside Missouri, others rallied in Brown's memory and called for change.
Hundreds of people demonstrated in and around the US capital Washington, including some who laid on the ground for several minutes in a "die in" at a shopping mall near the Pentagon.
- 15 arrests in Ferguson -
The peaceful march came after 15 protesters were arrested late Friday outside the Ferguson police department and after demonstrators shut down a shopping mall in St Louis, demanding a boycott of post-Thanksgiving shopping.
Monday's announcement that Wilson will not face charges sparked looting, arson and gunfire in parts of Ferguson, a mainly black suburb with a mostly white police force.
The NAACP wants police to use body cameras, changes to the system of equipping police with military hardware, a promotion of diversity on the force and an end to the use of major force in cases involving minor offenses.
Adrian West, a technology trainer, waited nearly two hours for the marchers to show up late, potentially missing a memorial service for a friend killed in a fight.
But he still expressed support, hopeful that nationwide protests would yet bring change.
"I think this is enough to get the federal government's attention, strong enough to make them listen, and it's quite possible Darren Wilson could end up getting indicted by the federal government."
A federal probe into whether Wilson violated Brown's civil rights is ongoing.