The shooting of Brown, who was black and unarmed at the time, by a white police officer led to days of protests. Brown's death has raised once again old questions about the relationship between law enforcement and the black community in urban and surburban communities, revealing just how differently whites and blacks see life in America.

Missouri Gov. Jay Nixon declared a state of emergency in Ferguson, Mo. several days ago, as businesses, schools and residents braced for potentially violent protests, like those that followed the August shooting. (Here's the Post's live blog.)

Some of the questions that Brown's death has raised simply don't have answers, but here are a few things you might be wondering about if you're just getting caught up on what's happening in Ferguson right now.

-- What did the grand jury decide in Ferguson?

-- Is the grand jury's decision final?

-- What happened overnight in Ferguson?

-- What do we know about the shooting?

-- Were Brown's hands up when he was shot?

-- How does the public feel about this case?

-- How common are police shootings?

-- What do the protesters want?

-- Is there a song that conveys protesters' grievances?

-- Why do police officers in Ferguson look like soldiers?

-- Has President Obama said anything since the announcement?

After reviewing the evidence, the grand jury "determined that no probable cause exists to file any charge against Officer Wilson,” said prosecuting attorney Robert P. McCulloch. “They are the only people who have heard and examined every witness and every piece of evidence.”

The grand jury — composed of 12 ordinary citizens, three of whom are black — had been reviewing conflicting information from several eyewitnesses and three autopsy reports. Nine jurors would have had to vote to charge Wilson for him to be indicted, at which point he would have an opportunity to defend himself before a judge and a jury in a trial. Go here if you have more questions about grand juries.

The jurors could have chosen to indict Wilson on one or more of five charges -- from murder in the first degree to involuntary manslaughter. While there was no question that Wilson killed Brown, McCulloch said, a key question was whether Wilson was authorized "to use deadly force" to defend himself under the law. The law offers police fairly wide latitude to defend themselves if they believe they are facing imminent danger. The grand jury returned what is known as a "no-true bill" for each of the five charges.

Few expected Wilson to be charged. Many experts say the governing law, established by the Supreme Court three decades ago, allows police officers to shoot to kill as long as they believe their lives are in imminent danger — which Wilson has said he believes was the case.

Many people moved by Brown's death argued that Wilson should be charged, and public opinion polling suggested that was a widely held view.

Brown's family and many members of the public will also be looking through the case files that were released with the announcement of the grand jury's decision.

The federal government is also conducting separate investigations. Wilson himself is the subject of one probe. The FBI, along with the St. Louis County police, is gathering evidence to determine whether the officer violated Brown's civil rights when he shot him. That's a very hard thing to prove, and The Washington Post has reported that civil rights charges against Wilson are unlikely.

The other investigation focuses on the Ferguson Police Department in general. The feds are trying to see whether there is a pattern of racial bias in how the department conducts its operations.

In any case, Wilson has agreed to resign from the force. There are also reports that Chief Thomas Jackson could leave his post, and that the entire force could be dissolved and replaced with county patrols.

At this point, it looks like two dozen buildings in Ferguson and a couple of police vehicles burned overnight. One photograph showed cars on fire in a dealer's lot. Most of those fires have been extinguished.

Storefront windows were smashed. For a while, a crowd was blocking the interstate, and shots were fired. Police made 61 arrests and fired tear gas canisters to disperse crowds.

But looting appears to be minimal so far, The Post reports, and police have said they know of no injuries except for one person whose car was hijacked.

Protest leaders and police officers had been meeting regularly to plan the demonstrations so that both sides would know when to draw the line. Many people are probably thinking back to the riots in Los Angeles in 1992, when vandalism and assault were widespread and fires burned out of control. Business and law enforcement officials warned that the protests that would inevitably follow a decision not to indict could become violent. For their part, demonstrators are worried that police will respond disproportionately, and they'd been stocking up on items like shatter-proof goggles to protect themselves from tear gas.

The images from Ferguson we've received so far have certainly been chaotic, but as The Post's Wesley Lowery and David Montgomery write, "The majority of protesters were peacefully passionate." They report that after an eerie silence in which protesters listened, rapt, to McCulloch's announcement, the crowd chanted and taunted police. Some threw water bottles.

Just after 12 p.m. on Aug. 9, Wilson was driving along Canfield Dr. in his police vehicle, a Chevy Tahoe. A little while ago, he had heard over the radio that two people had just stolen cigarillos from a convenience store nearby off West Florissant Ave, one of whom was in a red hat and yellow socks. Surveillance footage from the store appears to show Brown and a friend, Dorian Johnson, stealing from the store that morning.

Brown and Johnson were walking in the street toward Wilson's car on Canfield. Monday night, McCulloch, the county prosecutor, gave an account of what happened when the officer met the two men, which has been much disputed:

As Wilson slowed or stopped, as he reached Mr. Brown, he told him to move to the sidewalk. Words were exchanged and they continued walking down the middle of the street. As they passed, Wilson observed that Michael Brown had cigarillos in his hand and was wearing a red hat and yellow socks.

At approximately 12:02 p.m., Wilson radioed that he had two individuals on Canfield and needed assistance. Officer Wilson backed his vehicle at an angle blocking their path and blocking the flow of traffic in both directions. Several cars approached from both east and west but were unable to pass the police vehicle.

An altercation took place at the car with Officer Wilson seated inside the vehicle and Mr. Brown standing at the driver's window. During the altercation, two shots were fired by Officer Wilson while still inside the vehicle. Mr. Brown ran east on Canfield and Officer Wilson gave chase.

Near the corner of Canfield and Copper Creek, Mr. Brown stopped and turned back towards Officer Wilson. Officer Wilson also stopped. Michael Brown moved toward Officer Wilson, several more shots were fired by the officer, and Michael Brown was fatally wounded. Within seconds of the final shot, the assist car arrived. Less than 90 seconds passed between Officer Wilson's first contact with Michael Brown and his companion and the arrival of that assist car.

Here's a video telling the story of Michael Brown's death.

Wilson told the grand jury that Brown had prevented him leaving the car by leaning against the door and then began hitting him inside the car. Wilson said he couldn't reach his baton, that his pepper spray would have blinded him as well, and that he wasn't carrying a taser. Wilson drew his firearm, but said that Brown managed to grab it.

"I was guaranteed he was going to shoot me," Wilson said in an interview released along with the evidence. "He had completely overpowered me while I was sitting in the car." Wilson said he was worried that if Brown hit him again, he could have lost consciousness. He had already radioed for assistance.

Previous public statements by witnesses, including Johnson, have contradicted some portions of this account. Johnson, for example, told The Post through an attorney that Wilson was the aggressor, grabbing Brown by the neck through the open window of his car. He also said that when Brown stopped running, he was trying to surrender and raising his hands.

McCulloch, the prosecutor, said that many witnesses had given inconsistent statements or statement that contradicted the evidence. For example, many people said initially that they had seen Wilson shoot Brown from behind, but the autopsies showed that Brown had not been shot in the back.

Many people have heard that Brown's hands were up when he was shot, and demonstrators have been raising their hands as a sign of protest. McCulloch said that witnesses gave conflicting testimony about where Brown's hands were.

"Some witnesses maintained their original statement that Mr. Brown had his hands in the air and was not moving toward the officer when he was shot," he said. "Several witnesses said Mr. Brown did not raise his hands at all or that he raised them briefly and then dropped them and then turned toward Officer Wilson, who then fired several rounds."

What exactly happened in the minute before Brown's death might be one of those questions to which we never know the answer.

Two nights after Brown's death, a crowd gathered for a candlelight vigil turned unruly, and several local businesses were looted. Over the following few nights, police responded to protests in riot gear, using tear gas to disperse crowds of demonstrators. The protests attracted media attention from around the world.

Nixon later declared a state of emergency, sent in the National Guard and placed a black highway patrol captain in charge of responding to the protests. Only with Attorney General Eric Holder's visit to Ferguson 12 days after the shooting did tensions begin to ease.

A Pew poll after the shooting found that people's views on Brown's death depended on their own race. Four in five blacks agreed that the shooting raises important questions about race, compared to only 37 percent of whites. By contrast, almost half of whites said that race was getting too much attention in the discussion of Brown's death.

This division isn't especially surprising. Whites tend to believe that discrimination in the United States is more or less over — and the ones who do think it is a problem tend to be concerned about discrimination against whites, research shows.

Headlines about police shootings are frequent. Over the weekend, for example, police shot and killed a 12-year-old boy carrying a BB gun in Cleveland.

But this is another hard question to answer. There is no comprehensive database on officer-involved shootings, although the federal government collects data on all kinds of crimes.

Here's one: "Hands Up" by Vince Staples (Def Jam Recordings).

The lyrics focus on police brutality in Los Angeles, but Staples released the song about a month after the shooting in Ferguson, and the title could be an allusion to a chant that's become popular with demonstrators there.

They're angry that Brown is dead, to be sure, but there are plenty of other problems in the suburbs of St. Louis that are probably contributing to the tensions there.

About two-thirds of Ferguson's residents are black, and the poverty rate is 22 percent, according to the census. In this regard, it isn't unlike many other poor, suburban communities around the country where most residents are people of color. Places like Ferguson were forged by decades of government policies and unofficial industry practices that limited black residents to certain areas of major cities.

The federal government built segregated public housing and provided subsidies and loans to developers if they agreed to build segregated neighborhoods in St. Louis, as in other cities. Local authorities prohibited liquor stores and other unsavory establishments from setting up shop in white neighborhoods, concentrating them where blacks lived. The utilities neglected those districts, too.

Ferguson was initially created to exclude blacks, but as blacks moved in, whites gradually left. One reason was likely that they knew that black neighborhoods were poorer and did not want to live in one. Far fewer blacks live in segregated neighborhoods now than even 20 years ago, but they are still twice as likely as whites to live in neighborhoods where almost all residents are black.

Ferguson police are about three times as likely to arrest blacks as whites, a disparity that is typical for many police departments, according to an analysis by USA Today.

One thing that does make Ferguson unusual is the fact that despite its large black population, the city council has only a single black member. And local government relies heavily on money from traffic tickets and court fees to pay its bills, which makes residents suspicious of the cops.

Finally, there's the fact that police in Ferguson responded to the initial protests with military equipment —  mine-resistant armored vehicles, rifles and combat fatigues. Holder said at the time that by responding in force, local law enforcement risked further eroding the community's trust.

The federal government, it turns out. The Pentagon, for example, transferred surplus military equipment worth close to half a billion dollars to local law enforcement agencies last year, including everything from armored vehicles to dog goggles and bouncy castles.

Another resource is the cash and property police seize from suspects — although officers generally don't have to prove that the people whose stuff they seize are guilty of a crime.

The White House has said it will review these programs.

He has said that the grand jury's decision must be accepted. "We are a nation built on the rule of law. So, we need to accept that this decision was the grand jury's to make," he said.

He also asked protesters to demonstrated peacefully, repeating what Brown's father requested after the announcement.

The president said that, throughout the country, it's important to about  how to make sure African Americans are treated more equitably by law enforcement and the criminal justice system. "There are issues in which the law too often feels as if it is being applied in a discriminatory fashion," he said.

newsletters@email.washingtonpost.com