FERGUSON, Missouri (CNN) -

An evening of peaceful protests devolved into another tense standoff as a few protesters hurled bottles toward police in Ferguson, Missouri.

But the rowdy demonstrators were greatly outnumbered by fellow protesters trying to keep the gathering peaceful. Some locked arms and walked through the crowd.

"Get out of street! Don't fight!" some protesters bellowed on bullhorns.

Police in riot gear formed a barricade, donnning gas masks and asking reporters to do the same. Some sat with guns pointed atop armored vehicles. But they showed restraint.

Officials temporarily detained a few, including news photographer Scott Olson and longtime activist and Holocaust survivor Hedy Epstein.

"We are not going to let outside provocateurs to come here. We can't allow this movement to be destroyed," said Malik Shabazz, national president of Black Lawyers for Justice.

The renewed tensions came after the preliminary results of an autopsy that Brown's family requested were released, as was a new account of what allegedly happened in the moments immediately before the teenager was killed by a local police officer.

Evidence in the shooting death could be presented to a grand jury as early as Wednesday.

And as the situation in the St. Louis suburb was being watched and talked about across the country, it continued to draw comments from numerous quarters -- including the White House.

"We have all seen images of protesters and law enforcement in the streets. It's clear that the vast majority of people are peacefully protesting. What's also clear is that a small minority of individuals are not," said President Barack Obama.

"While I understand the passions and the anger that arise over the death of Michael Brown, giving into that anger by looting, or carrying guns, and even attacking the police only serves to raise tensions and stir chaos," he said, in a call for calm.

"Let's see some understanding" rather than confrontation, and "let's seek to heal," the President said.

Brown's death has sparked nightly protests in the Ferguson, prompting Gov. Jay Nixon to call out the National Guard.

Dueling narratives

The officer who killed Brown says the teenager rushed at him full speed in the moments before the shooting, according to an account phoned in to a St. Louis radio station and confirmed by a source with detailed knowledge of the investigation.

According to the version on KFTK, phoned in by a woman who identified herself as "Josie," the altercation on August 9 began after Officer Darren Wilson rolled down his window to tell Brown and a friend to stop walking in the street.

When Wilson tried to get out of his cruiser, Brown first tried to push the officer back into the car, then punched him in the face and grabbed for his gun before breaking free after the gun went off once, the caller said.

Wilson pursued Brown and his friend, ordering them to freeze, according to the account. When they turned around, Brown began taunting Wilson, saying he would not arrest them, then ran at the officer at full speed, the caller said.

Wilson then began shooting. The final shot was to Brown's forehead, and the teenager fell two or three feet in front of Wilson, said the caller, who identified herself as the officer's friend.

A source with detailed knowledge of the investigation later told CNN the caller's account is "accurate," in that it matches what Wilson has told investigators.

But accounts of exactly what happened when Wilson stopped Brown vary widely.

Witnesses said they saw a scuffle between the officer and Brown at the police car before the young man was shot. Several witnesses said Brown raised his hands and was not attacking the officer.

Piaget Crenshaw said she was sitting in her home when she witnessed the shooting. She captured video of the aftermath, including images of Brown's body lying in the middle of the street.

Crenshaw said Brown was running away from police and then turned around. She said that was when Brown was shot.

Police provided a different narrative, saying Brown struggled with the officer and reached for his weapon.