In the days since an unarmed black teenager, Michael Brown, was shot to death by a white police officer here on Aug. 9, an array of state and local law enforcement authorities have swerved from one approach to another: taking to the streets in military-style vehicles and riot gear; then turning over power to a Missouri State Highway Patrol official who permitted the protests and marched along; then calling for a curfew.
Early Monday, after a new spate of unrest, Gov. Jay Nixon said he was bringing in the National Guard. Hours later, he said that he was lifting the curfew and that the Guard would have only a limited role, protecting the police command post.
Although the tactics changed, the nighttime scene did not.
Captain Johnson, who is coordinating security operations, gave no sense of whether the police would change their tactics again on Tuesday. But he urged peaceful protesters to demonstrate during daylight hours so as not to give cover to “violent agitators,” and he pledged, despite the repeated nights of tumult, “We’re going to make this neighborhood whole.”
Adding to the turbulence was confusion over the curfew. Although it was no longer in force, the police demanded around midnight that the crowd disperse, a move the authorities attributed to increasingly unsafe conditions.
Also on Monday, more details emerged from autopsies performed on Mr. Brown’s body. One showed that he had been shot at least six times; another found evidence of marijuana in his system.
In Washington, President Obama said that Attorney General Eric H. Holder Jr. would go to Ferguson on Wednesday to meet with F.B.I. agents conducting a federal civil rights investigation into the shooting. He seemed less than enthusiastic about the governor’s decision to call in the National Guard.
He added that he would be closely monitoring the deployment.
He again tried to strike a balance between the right to protest and approaches to security.
“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,” Mr. Obama said.
After more than an hour of peaceful protests, some in the crowd began to throw bottles at the police, who brought out armored vehicles and tactical units. But many peacekeepers in the crowd formed a human chain and got the agitators to back down.
At another point, as protesters gathered near a convenience store, some of them threw objects; the police responded with tear gas.
And near midnight, the police began announcing over loudspeakers that people needed to leave the area or risk arrest after what the police said were repeated gunshots and a deteriorating situation.
A few blocks away, at the police command post, National Guard members in Army fatigues, some with military police patches on their uniforms, stood ready but never entered the area where protesters were marching. State and local law enforcement authorities oversaw operations there.
Residents seemed puzzled and frustrated by the continually changing approaches, suggesting that the moving set of rules only worsened longstanding tensions over policing and race in this town of 21,000.
“It almost seems like they can’t decide what to do, and like law enforcement is fighting over who’s got the power,” said Antione Watson, 37, who stood near a middle-of-the-street memorial of candles and flowers for Mr. Brown, the 18-year-old killed on a winding block here.
“First they do this, then there’s that, and now who can even tell what their plan is?” Mr. Watson said. “They can try all of this, but I don’t see an end to this until there are charges against the cop.”
The latest turn in law enforcement tactics — the removal of a midnight-to-5 a.m. curfew imposed Saturday and the arrival of members of the Guard — followed a chaotic Sunday night. Police officers reported gunfire and firebombs from some people among a large group, and they responded with tear gas, smoke canisters and rubber bullets.
By Monday, the police seemed intent on taking control of the situation long before evening and the expected arrival of protesters, some of them inclined to provoke clashes. The authorities banned stationary protests, even during the day, ordering demonstrators to continue walking — particularly in an area along West Florissant, not far from where the shooting occurred. One of those told to move along was the Rev. Jesse L. Jackson.
Six members of the Highway Patrol, plastic flex-ties within easy reach, stood guard at a barbecue restaurant that has been a hub of the turmoil. Just north of the restaurant, about 30 officers surrounded a convenience store that was heavily damaged early in the unrest. Several people were arrested during the day, including a photographer for Getty Images, Scott Olson, who was led away in plastic handcuffs in the early evening.
Explaining his decision to call in the National Guard, Mr. Nixon recounted details of the unrest on Sunday night and described the events as “very difficult and dangerous as a result of a violent criminal element intent upon terrorizing the community.”
Yet Mr. Nixon also emphasized that the Guard’s role would be limited to providing protection for the police command center, which the authorities say was attacked. Gregory Mason, a brigadier general of the Guard, described the arriving troops as “well trained and well seasoned.”
“With these additional resources in place,” said Mr. Nixon, a Democrat in his second term, “the Missouri State Highway Patrol and local law enforcement will continue to respond appropriately to incidents of lawlessness and violence and protect the civil rights of all peaceful citizens to make their voices heard.”
A recent survey by the Pew Research Center for the People and the Press showed that Americans were deeply divided along racial lines in their reaction to Mr. Brown’s killing. It showed that 80 percent of blacks thought the case raised “important issues about race that need to be discussed,” while only 37 percent of whites thought it did.
Blacks surveyed were also less confident in the investigations into the shooting, with 76 percent reporting little to no confidence, compared with 33 percent of whites.
Supporters of Darren Wilson, the Ferguson police officer who fired the fatal shots, gathered outside a radio station in St. Louis over the weekend.
Mr. Brown is now the subject of three autopsies. The first was conducted by St. Louis County, and the results were delivered to the county prosecutor’s office on Monday. That report showed evidence of marijuana in Mr. Brown’s system, according to a person briefed on the report who was not authorized to discuss it publicly before it was released.
Another autopsy, on Monday, was done by a military doctor as part of the Justice Department’s investigation.
On Sunday, at the request of Mr. Brown’s family, the body was examined by Dr. Michael M. Baden, a former New York City medical examiner.
Dr. Baden’s autopsy showed that Mr. Brown was shot at least six times in the front of his body and that he did not appear to have been shot from very close range, because no powder burns were found on his body. But that determination could change if burns are found on his clothing, which was not available for examination.
In a news conference on Monday, family members and Dr. Baden said that the autopsy confirmed witness accounts that Mr. Brown was trying to surrender when he was killed.
Daryl Parks, a lawyer for the family, said the autopsy proved that the officer should have been arrested. The bullet that killed Mr. Brown entered the top of his head and came out through the front at an angle that suggested he was facing downward when he was killed, Mr. Parks said. The autopsy did not show what Mr. Brown was doing when the bullet struck his head.
“Why would he be shot in the very top of his head, a 6-foot-4 man?” Mr. Parks said. “It makes no sense. And so that’s what we have. That’s why we believe that those two things alone are ample for this officer to be arrested.”
Piaget Crenshaw, a resident who told reporters that she had witnessed Mr. Brown’s death from her nearby apartment, seemed unsurprised by the eruptions of anger, which have left schools closed and some businesses looted. “This community had underlying problems way before this happened,” Ms. Crenshaw said. “And now the tension is finally broken.”
For businesses here, the days and long nights have been costly and frightening. At Dellena Jones’s hair salon, demonstrators tossed concrete slabs into the business as Ms. Jones’s two children prepared for what they had expected to be a first day back to school.
“I had a full week that went down to really nothing,” she said of her business, which has been mostly empty. “They’re too scared to come.” As she spoke, a man walked by and shouted, “You need a gun in there, lady!”
In his news conference, Mr. Obama said that most protesters had been peaceful. “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.