Attorney General Eric H. Holder Jr. swept into this battle-scarred St. Louis suburb on Wednesday, meeting with community leaders and promising a “thorough and fair” federal inquiry into the police shooting death of an unarmed black teenager.

Before going into an investigative briefing at the local FBI headquarters, Holder said the Justice Department had assembled “very experienced” prosecutors and agents to determine whether 18-year-old Michael Brown’s civil rights were violated when he was shot by a white police officer.

“Our investigation is different” from a parallel St. Louis county probe, Holder said in a meeting room surrounded by his top aides and local federal officials. “We’re looking for possible violations of federal civil rights statutes.’’

Earlier Wednesday, the nation’s black attorney general offered a highly personal perspective on Brown’s death and the days of sometimes violent protests it has spawned in this predominantly black community of 21,000 people. “The eyes of the nation and the world are watching Ferguson right now,’’ Holder said after meeting with students at St. Louis Community College and hearing about their distrust of police.

“I understand that mistrust. I am the Attorney General of the United States. But I am also a black man,’’ Holder said, recalling his own humiliation when he was pulled over on the New Jersey Turnpike and accused of speeding by officers who searched his car. He also spoke of rushing to a movie in the District and being stopped by an officer, who flashed his lights and yelled “Where are you going? Hold it!”

“I was a federal prosecutor. I wasn’t a kid. I was a federal prosecutor. I worked at the United States Department of Justice. So I’ve confronted this myself,’’ Holder told more than 50 Ferguson community members in an auditorium at the community college.

Although he declined to provide details of the federal investigation into the Brown case, Holder concluded by saying: This country is capable of change. But change doesn’t happen by itself. So let’s start here. Let’s do the work today.”

Holder’s remarks, unusual for a federal law enforcement official overseeing an active case, pointed up the urgency with which the Obama administration views Brown’s death and the events in Ferguson, even as local officials said the community had reached a turning point after fewer protests Tuesday night. The Justice Department investigation has escalated in recent days, with more than 200 people interviewed by agents and prosecutors.

The state investigation of Brown’s death is also moving forward, as the St. Louis County prosecutor’s office on Wednesday presented the first pieces of evidence to a grand jury that will determine if state charges are filed against Officer Darren Wilson, who shot Brown on Aug. 9. It could take until October for the grand jury to hear all of the evidence, St. Louis County Prosecutor Robert McCulloch said. “We will present absolutely everything to this grand jury,” McCulloch told radio station 550-KTRS in St. Louis.

As Ferguson prepared for another night of possible protests, police releases the first set of comprehensive arrest figures for who they have taken into custody since the demonstrations started. The records showed that a total of 155 people have been arrested, 123 of them charged with refusal to disperse and a few on more serious counts such as unlawful use of a weapon.

Although 126 of those arrested were from Missouri, the records showed, the rest came from throughout the United States, including nine from Illinois, five from California and one from the District.

In Ferguson on Wednesday, many business were open on the downtown commercial strip on West Florissant Avenue. A small group of people were still protesting, watched warily by a small number of police officers.

Angry aftermath of the Missouri shooting

The relative calm came after another tense night Tuesday. About midnight, in the streets near where Brown was killed, bottles filled with ice and water were thrown at police. So was urine. Police said “agitators” hid behind journalists. Officers stormed a press area hunting for perpetrators. In all, 47 people were arrested — one for the third time since protests began.

But Capt. Ronald Johnson of the Missouri State Highway Patrol said a city torn by riots was beginning to heal.

“I believe there was a turning point made,” Johnson said during a news conference at about 2:30 a.m. Central time. He credited volunteers, activists, clergy and community “elders” with changing the tone of sometimes violent demonstrations.

“They walked, they talked with people,” Johnson said. “They urged order, calm and peace. That had a calming influence on the younger people.”

That calm preceded potential chaos. The night began with a procession chanting “Hands up, don’t shoot.” A group of elementary-school girls handed out flowers. Police were dispersed throughout the crowd, instead of facing down protesters in a long line.

At that point, only some officers seemed to be enforcing a rule that protesters could walk, but not stand still or congregate.

“I saw the police arrest a lady because she had stopped walking,” said Bryan Maynard, 35, who had come to see the protests firsthand Tuesday. It was his first night on West Florissant Avenue, the suburban thoroughfare that has become the scene of repeated nighttime clashes. “It’s more than heavy-handed.”

But the worst time in Ferguson has never been the early evening.

“At some point every night, it’s like a switch is flipped. Sometimes a rock gets thrown. An unruly march. A molotov cocktail,” said Jon Belmar, the St. Louis County police chief, early in the night.

Later, about 9:30 p.m. Central time, hundreds of people looped up and down the street, alternating chants of “We ready!” and “No justice, no peace, no racist police” and “We are Mike Brown.”

Near the center of the street stood Alerion Smith, a 6-year-old who waved in his hand a “know your rights” booklet.

His mother said that the other day he came up to her and said, unprompted: “Having your hands up means ‘Don’t shoot.’ It means surrender.” That was when she decided he was ready to see the protests for himself.

“Obvious this is something he had heard about and was affecting him,” said Alexis Simpson, 29. “So I decided to bring him out to see what is going on in his own neighborhood.”

About 10 p.m. Central time, TV cameras showed officers making arrests.

Markon and Nakamura reported from Washington. Wesley Lowery, DeNeen L. Brown and Emily Wax-Thibodeaux in Ferguson and Kimberly Kindy, Julie Tate and David A. Fahrenthold in Washington contributed to this report.