Story highlights Officer who shot Michael Brown treated for "swollen face," police say

Police, witnesses offer starkly contrasting accounts of Brown's shooting

Witnesses, Brown's friend say the officer opened fire after a verbal altercation

Police chief: Brown assaulted the officer and struggled with him over his weapon

It's a case of he said, he said. The accounts of why a police officer fatally shot Michael Brown on a street in Ferguson, Missouri, on Saturday couldn't be more disparate.

One side says the teenager was surrendering, his hands in the air to show he was unarmed, when the officer opened fire. Authorities counter that Brown attacked the officer in his car and tried to take his gun.

The St. Louis suburb of 21,000 was wracked by violence as protesters outraged over the 18-year-old's shooting faced off with police.

Although there were reports that some demonstrations were peaceful -- protesters held up their hands, as Brown reportedly did, and others demanded a fair inquiry, chanting, "No justice, no peace" -- there were also reports of fires, looting, vandalism and attacks on police officers.

As federal civil rights investigators and the FBI carry out their own inquiry into the case, tensions are running high in Ferguson, where there's a history of distrust between the predominately black community and the largely white police force.

JUST WATCHED Ferguson Police chief: We want the truth Replay More Videos ... MUST WATCH Ferguson Police chief: We want the truth 03:15

JUST WATCHED Teen shooting in Missouri sparks riots Replay More Videos ... MUST WATCH Teen shooting in Missouri sparks riots 02:14

JUST WATCHED Mom: 'You took my son away from me' Replay More Videos ... MUST WATCH Mom: 'You took my son away from me' 01:52

Brown was African-American. Police have not identified the shooter, but a witness told CNN on Tuesday that the officer who opened fire is a Caucasian male.

The dispute between distraught Ferguson residents and police isn't likely to be settled soon.

One thing is sure, though: What police say was self-defense by the yet-to-be-named officer doesn't jibe with the accounts of those who say they saw the encounter.

Here's what CNN has learned:

Brown was spending the summer in the neighborhood with his grandmother Desuirea Harris, she told CNN affiliate KMOV . She described him as "a good kid."

Family members say he was a recent graduate of nearby Normandy High School and was going to begin classes at Vatterott College on Monday.

Brown and a friend were walking to Harris' house, his mother and grandmother said, when a Ferguson police officer confronted them.

This is where the stories part ways.

Dorian Johnson, 22, told CNN that he and Brown were walking in the middle of the street when a white male officer pulled up and told them, "Get the f*** on the sidewalk." The young men replied that they were "not but a minute away from our destination, and we would shortly be out of the street," Johnson said.

The officer drove forward but stopped and backed up, almost hitting the pair, Johnson said.

"We were so close, almost inches away, that when he tried to open his door aggressively, the door ricocheted both off me and Big Mike's body and closed back on the officer," Johnson said.

Still in his car, the officer then grabbed Brown by his neck, Johnson said. Brown tried to pull away, but the officer kept pulling Brown toward him, he said.

JUST WATCHED Missouri City Erupts after Teen's Death Replay More Videos ... MUST WATCH Missouri City Erupts after Teen's Death 07:16

JUST WATCHED Police chief: 'We can get to the truth' Replay More Videos ... MUST WATCH Police chief: 'We can get to the truth' 02:32

JUST WATCHED Protests over teen's death turn violent Replay More Videos ... MUST WATCH Protests over teen's death turn violent 02:03

The officer drew his weapon, and "he said, 'I'll shoot you' or 'I'm going to shoot' " and almost instantaneously fired his weapon, hitting Brown, Johnson said.

Johnson and a bloodied Brown took off running, and Johnson hid behind the first car he saw, he said. The officer got out of his car.

"I saw the officer proceeding after my friend Big Mike with his gun drawn, and he fired a second shot and that struck my friend Big Mike," Johnson told CNN's Wolf Blitzer. "And at that time, he turned around with his hands up, beginning to tell the officer that he was unarmed and to tell him to stop shooting. But at that time, the officer firing several more shots into my friend, and he hit the ground and died."

"We wasn't committing any crime, bringing no harm to nobody, but my friend was murdered in cold blood," he told KMOV

Witness Tiffany Mitchell was picking up Piaget Crenshaw for work when she saw Brown and the officer "tussling through the window." Mitchell and Crenshaw concurred with Johnson, saying Brown appeared to be trying to pry himself away from the officer's grasp. Brown had his hand on the police cruiser, trying to push himself away, Mitchell said.

Mitchell reached for her phone to record the encounter.

"I didn't get the video because a shot was fired through the window so I tried to get out of the way," she said.

After that shot, Brown broke free from the officer's grasp, both women told CNN, and started running, but he only got about 20 feet from the squad car by Crenshaw's estimate.

"The cop gets out of his vehicle shooting," Mitchell said. "(Brown's) body jerked as if he was hit from behind, and he turned around and he put his hands up. ... The cop continued to fire until he just dropped down to the ground, and his face just smacked the concrete."

Added Crenshaw, who said she was watching the incident unfold from a nearby balcony, "The (officer) actually shot kind of carelessly. They shot my neighbor's building that was on the opposite side of the police car. They then later came and removed that bullet. ... Anybody could've been standing right there."

That Brown was unarmed is undisputed -- St. Louis County Police Chief Jon Belmar said every casing found at the scene was from the officer's weapon -- but he said at a Sunday news conference that Brown was not an innocent victim.

"The genesis of this was a physical confrontation," Belmar said, adding that Ferguson police asked his office to investigate the case.

Without revealing what led to the dispute, Belmar said the preliminary investigation showed that the Ferguson officer tried to exit his vehicle, but Brown pushed him back into the car, "where he physically assaulted the police officer" and struggled over the officer's weapon, Belmar said.

A shot was fired inside the police car, and Brown was eventually shot about 35 feet away from the vehicle, Belmar said.

JUST WATCHED Looting breaks out during protest Replay More Videos ... MUST WATCH Looting breaks out during protest 01:01

JUST WATCHED Ferguson mayor: Remain calm Replay More Videos ... MUST WATCH Ferguson mayor: Remain calm 02:47

JUST WATCHED Fatal police shooting sparks protests Replay More Videos ... MUST WATCH Fatal police shooting sparks protests 01:04

The officer was taken to an area hospital where he was treated for a "swollen face," Ferguson Police Chief Tom Jackson said, adding he had not personally seen the officer's injury.

He was released the same day. Jackson said he has spoken to the officer, who was "very shaken about what happened that day and the aftermath. ... He's hurt."

It's unclear how many times Brown was shot. Mitchell said it was "more than about five or six" times. Johnson said it was more than three, and Brown's mother said she was told he was shot eight times. Some witnesses said they heard as many as 10 shots. Belmar said only that it "was more than just a couple."

The chief didn't explain how Brown got so far away from the car or whether he was surrendering. He said he was declining to disclose certain details because he didn't want to "prejudice" the case.

The officer is on paid administrative leave. There's no word on when authorities will identify him, but Belmar said he has been with the force six years and is "unaware of any other issues that he's been involved in."

He will be required to undergo two psychological evaluations before returning to duty, the chief said.

Meanwhile, Brown's mother, Lesley McSpadden, didn't need to know his identity to direct some pointed words at the man who shot the son she knew as a "gentle giant."

"You're not God. You don't decide when you're going to take somebody from here," she told KSDK.