President Obama announced Monday that Attorney General Eric H. Holder Jr. will travel to Ferguson, Mo., to meet with law enforcement officials investigating the fatal shooting of unarmed teenager Michael Brown by a police officer. (AP)

President Obama announced Monday that Attorney General Eric H. Holder Jr. will travel to Ferguson, Mo., to meet with law enforcement officials investigating the fatal shooting of unarmed teenager Michael Brown by a police officer. (AP)

Attorney General Eric H. Holder Jr. will travel to this battle-scarred St. Louis suburb to oversee the investigation of the shooting death of an unarmed black teenager at the hands of a white police officer, the White House said Monday.

Holder’s visit was announced as National Guard troops arrived to back up local and state police. On Monday night in Ferguson, an early evening calm gave way to new confrontations as some demonstrators threw bottles at heavily armed police and officers threw stun grenades and tear gas towards them.

The day was expected to be a crucial test for everybody in charge here, from local police commanders to Missouri Gov. Jay Nixon (D) — who had called out the National Guard after chaotic protests Sunday — to President Obama himself. Obama’s decision to dispatch his attorney general was an admission that the teenager’s killing had become a symbol of something enormous: a test of the American justice system and the government’s ability to police the officers who police everyone else.

Monday was a test, too, for community leaders — including ministers — who had hoped to keep the protests peaceful and focused on the death of Michael Brown, 18.

“We’re helping the police. Please move out the street,” they said over bullhorns, urging the crowds to move back from police lines.

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But despite all their good intentions, darkness fell and Ferguson slipped back toward chaos.

“We feel boxed in,” said Kerry Green, 35, a St. Louis native who has been at the protests every night. As he spoke, he was looking at police lined up at an intersection in front of him, a few minutes before the tear gas began to fly.

Green said the events in Ferguson were about much more than one killing, mentioning other cases, including that of Eric Garner, a New York man who died after police put him in a chokehold last month.

“It’s more than Mike Brown,” Green said. “It’s for the man who got choked out in New York. It’s for Trayvon Martin. It’s for us riding down the street with three friends in the car and we get pulled over.”

Earlier in the day, in Washington, authorities said Holder would arrive in Ferguson on Wednesday and meet with some of the FBI agents and prosecutors investigating the case. They have interviewed more than 200 people, scouring the area where Brown was shot by Darren Wilson, an officer with Ferguson’s police department.

Also Monday, a St. Louis radio station reported that a woman had called to tell the officer’s side of the story. The station, KFTK, said the woman called herself Josie and said that the confrontation began when Wilson told Brown and a friend to stop walking in the street. The caller said Wilson then decided that the two fit the description of robbery suspects and sought to stop them.

The caller said the men fought near the car, then Brown went a distance away, turned and charged the officer. “He just started to come at him full speed,” the caller said. “And so he just started shooting, and he just kept coming. . . . The final shot was in the forehead, and he fell about two, three feet in front of the officer.”

CNN reported that this account seemed to match a version of events the officer gave to investigators.

Earlier Monday, Obama addressed the unrest in Ferguson in starkly emotional terms at the White House. “As Americans, we’ve got to use this moment to seek out our shared humanity that’s been laid bare by this moment,’’ he said. “The potential of a young man and the sorrows of parents, the frustrations of a community, the ideals that we hold as one united American family.’’

As he has before, Obama said that while most demonstrators are acting peacefully, “a small minority of individuals are not. While I understand the passions and the anger that arise over the death of Michael Brown, giving in to that anger by looting or carrying guns and even attacking the police only serves to raise tensions.”

One stark illustration that the Brown case has revealed doubts about the government’s ability to police the police: Three separate autopsies have now been conducted on the teenager’s body. One was done at the behest of St. Louis County, another by private pathologists at the behest of Brown’s family and a third by the U.S. military at the behest of Holder.

On Monday, the results of the county autopsy and the family autopsy were revealed.

The county’s review, released to state prosecutors late Friday, found that Brown had six gunshot wounds to the head and chest and was shot from the front, people familiar with the autopsy said. It also showed that Brown had marijuana in his system, they said.

Also Monday, two forensic pathologists hired by Brown’s family said their autopsy showed he was hit by at least six shots, one of which struck him at the top of the head and traveled downward through the brain. They said two wounds appeared to be “reentry” wounds. They said that there were no signs on Brown’s body of a struggle and that he did not appear to have been shot at close range because no gunshot residue was found on his body.

An attorney for the Brown family said the autopsy showed that the teenager was “trying to surrender” when he was shot, but the forensic pathologists — Michael Baden and Shawn Parcells — said they could not determine whether that was the case.

Baden, a former longtime medical examiner in New York City, said Brown could have survived all of his gunshot wounds except the one to the top of his head.

The federal government’s autopsy was conducted Monday. Its results have not yet been released.

In Ferguson, the governor canceled the city’s midnight-to-5 a.m. curfew after one chaotic day. The worst night yet had been Sunday, when protesters threw debris at police and officers fired tear gas at the crowd before the curfew even took effect. In Ferguson, Monday night began with a false calm. The side streets off West Florissant had been blocked with fencing, making it harder to reach the scene of earlier confrontations — and harder to leave.

As of 9 p.m. local time, police were standing back, letting protesters move. Some officers, borrowed from the city of St. Louis, handed out water. Somebody in the crowd gave out red roses in Brown’s honor. The crowd was full of white-collared clergy members.

But Ron Robinson, a major with the St. Louis city police, said he could not relax. “It’s not over,” he said before 8 p.m. local time. “It’s gonna get worse before it gets better.”

And it did, again.

A few hours later, a line of police had formed in front of a Family Dollar on West Florissant Avenue, using sirens to try to drive back the crowd. TV cameras showed officers standing up through the roof hatches of armored vehicles, carrying rifles. “If you are standing in the street you are unlawfully assembled and you are subject to arrest,” an officer yelled toward a boarded-up barbecue restaurant.

Members of the crowd pulled a “yield” sign out of the ground and stood in the middle of the street defying the law enforcement officer’s instructions.

Later, just before 11 p.m. local time, a confrontation broke out near the burned-out remains of a Quik Trip convenience store — destroyed in the aftermath of Brown’s death. Dozens of men and women stood at the darkened Quik Trip parking lot. Some held their hands up. A police helicopter flew low overhead.

“If you are on the Quik Trip parking lot, you are unlawfully assembled. You need to continue to move,” an officer said .

The protesters stayed, and set up orange cones. Police responded by throwing out smoke bombs and flares, which engulfed TV reporters in the middle of their liveshots. West Florissant filled with smoke. Demonstrators pulled porta-potties into the middle of the roadways. Around midnight local time, the crowd had thinned down to a few clusters of people — including many members of the media. TV cameras showed a few protesters being arrested after refusing police commands to clear the road.

“Some of the media be like we provoking this. We standing on the sidewalk. They trained automatic weapons on us. [Protesters] threw a water bottle. That’s it,” said Carl Brown, a 26-year-old demonstrator.

Fahrenthold reported from Washington. DeNeen L. Brown in Ferguson, Mo., and Jerry Markon, David Nakamura, Adam Goldman, Mark Berman, Abigail Ohlheiser, Sari Horwitz, Kimberly Kindy, Alice Crites and Katie Zezima in Washington contributed to this report.