A wall of police officers faced off against protesters along Baton Rouge's East Boulevard on July 10. "She has a poster, you have a shotgun," one protester yelled as police rushed onto yards and sidewalks to arrest the demonstrators. (TWP)

A wall of police officers faced off against protesters along Baton Rouge's East Boulevard on July 10. "She has a poster, you have a shotgun," one protester yelled as police rushed onto yards and sidewalks to arrest the demonstrators. (TWP)

On the first two nights after Alton Sterling was pinned to the ground and fatally shot by police, people gathered peacefully and purposefully around the Triple S convenience store, where Sterling had been selling CDs when a call came in to 911 that a man in a red shirt had threatened someone with a gun.

Young people sat on cars with music streaming out open windows, waved some placards and generally commiserated, while sipping beer. The police were nowhere in sight. They seemed to be maintaining a respectful distance.

Then came the idea to take the protest to police headquarters Friday evening, where temporary steel barricades had been erected to wall off the building, even before a Dallas gunman struck down 12 police officers, killing five, during the end of a peaceful march through that city.

Riot police appeared, their faces covered with plastic masks. Protesters couldn’t understand a word of what they were supposed to do, or where police wanted them to go, they said in interviews. Soon, more than 30 had been arrested, and by Saturday night, they arrested some 102 more, most for the charge of obstructing public property.

Black Lives Matter activist ­DeRay Mckesson made sure his arrest was streamed live on Periscope, and as that virally spread, the behavior of this capital city’s police officers became the latest flash point in the angry and polarized debate over policing and race.

1 of 41 Full Screen Autoplay Close Skip Ad × The scene in Baton Rouge after a police officer fatally shoots a black man View Photos A video captured the shooting of Alton Sterling, 37. Outrage spread across the city. Caption A video captured the shooting of Alton Sterling, 37. Outrage spread across the city. July 11, 2016 Dakeria Anderson, 9, protests with the help of her sisters D'liyah, 6, and D'anyriah, 8, across the street from the Triple S market. The girls’ father, Dewayne Anderson, said that he had been protesting since the beginning and the girls wanted to know what it was all about. Bonnie Jo Mount/The Washington Post Buy Photo Wait 1 second to continue.

Early Sunday evening, even after the Louisiana governor and city police chief gave stern warnings about violence and defended police tactics, the protests and arrests began again. A group of about 200 marched toward an interstate, shouting “No justice, no peace!” as officers in helmets and tactical gear watched. At least 12 more were arrested, officials said.

“We don’t question people’s right to peacefully assemble or protest, and we’re going to protect that right,” said East Baton Rouge Sheriff Sid J. Gautreaux III. “But in the same token, we made it clear that we aren’t going to tolerate any lawlessness. We’re not going to tolerate any violence or destruction.” Officials said two officers were injured Saturday during the protests; one had several teeth knocked out by projectiles.

Of the two cities where black men were killed by police last week, this city has been the one that caused concern, both within the Justice Department and among the activists of a movement to change how police treat African Americans.

The Justice Department moved with urgency to take over the investigation into the two police officers involved in Sterling’s death, with Louisiana Gov. John Bel Edwards (D) announcing that decision the very day the news of the slaying first spread. Minnesota Gov. Mark Dayton (D) also asked for federal intervention after the death Wednesday of Philando Castile outside St. Paul, but officials said they will not do so right now.

Black Lives Matter activists worried that this swampy state capital, with its history of slavery and civil rights struggle, could be the next Ferguson, Mo. — another medium-size U.S. city with a predominantly black population and a predominantly white police force ill-equipped or unwilling to respond to the grievances of black Americans, or deal with protests for better rights.

Reports from Friday and Saturday from reporters on the scene indicated as much. When protesters moved their demonstration to the street outside of police headquarters on Friday night, police met them in riot gear, pounding on shields with their batons to make a deafening and repetitive thud.

Police had no megaphone or bullhorn as they ordered protesters to stay on the grass and out of the street. Police arrested 31 people that night, nearly all of them after they stepped into the roadway and were rushed by police and dragged away to police wagons.

Protesters against police violence in Baton Rouge were arrested after police officers were hit with objects on July 10. More than 100 demonstrators were arrested the night before, as anger at police shootings mounts. (Reuters)

On Saturday night, the People’s New Black Panther Party, a radical black nationalist group, arrived, and police formed a human chain, pushing the crowd back but with little instruction. An officer standing in the turret of an armored vehicle clutched a rifle. Dozens more were arrested, bringing the total to 102.

Kira Marrero, 22, who had driven to Baton Rouge from New Orleans and was one of the first demonstrators arrested Saturday night, said a police officer pointed an assault rifle at her shortly before her arrest.

“I was scared for my life,” she said. The officer “didn’t say anything to me.” Police also appeared overwhelmed as they ran out of blankets and handcuffs for all the prisoners at the jail, she said.

Seven weapons were confiscated in protests, Gautreaux said, adding, “We didn’t have any aggression with weapons towards the officers at all.”

Human rights group Amnesty International sent an open letter to the Baton Rouge police department Sunday, urging it to use more restraint and respect the rule of law in dealing with protesters.

“We would remind you that police authorities are required to act in accordance with international human rights standards and the U.S. Constitution,” the letter read. “Specifically, law enforcement must ensure that any decision to disperse an assembly is taken only as a last resort and carefully in line with the principles of necessity and proportionality.”

Officials offered a different narrative. Gov. Edwards, who comes from a family of sheriffs, said he was “very proud” of how the state’s agencies had responded and thought their response was “moderate.”

For the locals, this mass showing was a long time coming. Activists said the discrimination and police abuse have been so entrenched here for so long that it was time to stand up and say something.

“The bottom line is Baton Rouge is bad,” said Judy Whitney Davis, 51, who describes herself as the third generation of proud civil rights activists. Her parents were the children of sharecroppers who went to college and marched in the civil rights movement. Her grandfather set a building on fire as the Ku Klux Klan was meeting there. Her kids grew up on stories of struggle and perseverance. “And in 2016, I thought it’d be over by now,” she said. Instead, she finds herself advising them to protest — “and how not to die.”

“The South has been involved in racial injustice for generations,” said Joe Connelly, the pastor at Wesley United Methodist Church, which served as the starting point for Sunday afternoon’s protest march. “They said the South would ‘rise again,’ and they didn’t know it would come like this.”

On Sunday, Edwards affirmed a right to peaceable protest and pledged to reform policing practices.

“In our state and throughout the country, peaceful protests and demonstrations have been in the past and are presently and certainly in the future can be a force for good,” Edwards said. “And I can assure everyone that we are hearing the protesters.”

“We’re going to have to reevaluate where we are, in the way that we recruit and train officers, in the way we retrain them,” he said, “to make sure we can de-escalate situations and that the use of deadly force is not employed as often going forward. I think there are ways to do that; to pretend that there is not would do a disservice to everyone.”

A few hours later, protesters had blocked the streets once more, and police were again confronting how to balance the right of free assembly with the right of public access.

Wesley Lowery in Washington contributed to this report.