Days after an unarmed teen was shot to death in the St. Louis suburb of Ferguson, Missouri, few questions have been answered, raising tensions in the small, predominantly black city and prompting outrage from activists nationwide. Here is what we know about the killing of Michael Brown, 18.

What happened?

Brown was walking down the street with a friend when he was shot to death by a Ferguson police officer on Saturday afternoon, all parties acknowledge, but the facts surrounding his killing are hazy.

The friend, Dorian Johnson, 22, told msnbc the officer drove up to them and told them to "get the f--k on the sidewalk" and then braked in front of Brown. Johnson said the officer threatened, "I'm gonna shoot you." He fired multiple shots, Johnson said, as Brown ran for his life, stopping at one point with his hands up in surrender and yelling, "I don't have a gun, stop shooting!" But the bullets hit Brown, who collapsed onto the ground. Other witnesses corroborate Johnson's story, saying that Brown had his hands raised as the officer repeatedly fired at him.

Michael Brown, 18, was killed in Ferguson, Mo., near St. Louis on Saturday, Aug. 9. Facebook

Police paint a less peaceful account of the moments leading up to the shooting. They say a fight broke out after the officer asked the two to move to the side, and say the officer's gun went off inside the patrol car. They have not said why the officer approached the men in the first place. Police say there isn't any security camera footage from nearby buildings or police dashcam video of the incident.

Who was the officer involved?

Police have not identified the name or race of the officer in the shooting, despite protesters' calls for his identity to be made public. On Tuesday, a police spokesman cited safety reasons for not disclosing the information, saying threats had been made on social media to the officer. Witnesses have said it was a white policeman; Brown was black. The officer has been placed on administrative leave while the nearby, and bigger, St. Louis County police department investigates the incident. The FBI has opened a parallel investigation.

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Who was Michael Brown?

Brown, nicknamed "Big Mike" by friends, was two days away from his first day at a technical college. His father, Michael Brown Sr., told the Associated Press his son was "funny, silly, he would make you laugh." The teen had just graduated from high school on Aug. 1, using the summer to finish the last credits he needed. Neighbors and friends say he liked throwing around a football with friends, enjoyed rapping as a hobby, and planned to become a heating and air conditioning engineer.

"He was never a person who liked confrontation," Markese Mull, a neighbor, told the AP. "His smile was going to make you smile."

What has the reaction been?

The case immediately drew parallels to the 2012 death of Trayvon Martin, the unarmed black Florida teen shot to death by neighborhood watch volunteer George Zimmerman. In Ferguson, tensions boiled over: On Sunday night, the city was overrun by riots and looting. About three dozen people were arrested, and one convenience store was burned almost to the ground. Protesters chanted "Kill the police!" and "No justice, no peace." On Monday, a second night of unrest rocked the town, with police firing tear gas and rubber bullets to quell the crowd. The FAA approved a no-fly zone over Ferguson on Tuesday and police in riot gear faced off with protesters for a third night. County police said a woman was shot in the head in an apparent drive-by-shooting. A police officer was also involved in the shooting of an allegedly armed man near where civil-rights activist Rev. Al Sharpton spoke, NBC station KSDK reported. It was not immediately clear if either incident was related to the unrest.

But anger over the shooting is not just local: On Monday night, the local NAACP hosted a forum attended by hundreds in a Ferguson church, and national NAACP President Cornell William Brooks asked residents to "turn your anger into action."

Sharpton, president of the National Action Network and an msnbc host, traveled to Ferguson on Tuesday to meet with Brown's family and led a rally at the evening protest. Meanwhile, on Twitter, the hashtag "#TheyGunnedMeDown" emerged in response to media portrayals of the incident, and a “national moment of silence” is being planned through a Facebook campaign for Thursday.

What's next?

The St. Louis County Police Department is in charge of the investigation, and the FBI is doing a separate investigation to look into potential civil rights violations. No timeline for the investigation has been declared.

The Ferguson police chief has said it will not release the name of the officer involved in the shooting unless charges are filed or a judge orders the disclosure.

Brown's family has retained Benjamin Crump, the same attorney who represented Trayvon Martin's family, but has not filed a lawsuit at this point.

"I don't want to sugarcoat it," Crump said. "(Brown) was executed in broad daylight."

In a press conference Tuesday, Crump and Sharpton urged peaceful protests, saying Brown's family had called for calm.

"To become violent in Michael Brown's name is to betray the gentle giant that he was," Sharpton said. "Don't be so angry that you distort the image of who his mother and father told us he was."