The officer was placed on administrative leave Saturday after fatally shooting 18-year-old Michael Brown in Ferguson, where the case has stoked racial tension, rallies and a night of looting. Police say death threats prompted them to withhold the officer's name.
Investigators have released few details, saying only that the shooting was preceded by a scuffle between the officer and a man in which the officer's weapon fired inside a patrol car. Witnesses say Brown had his hands raised when the officer repeatedly shot him in the predominantly black city of about 21,000 residents.
"The local authorities have put themselves in a position — hiding names and not being transparent — where people will not trust anything but an objective investigation," Sharpton, standing with Brown's parents, said during a news conference in St. Louis.
He also echoed pleas for peaceful protests by the NAACP and Brown's father, Michael Brown Sr., who told the crowd: "I need all of us to come together and do this right. ... No violence." President Barack Obama released a statement also urging calm, saying people must comfort each other "in a way that heals, not in a way that wounds."
Ferguson Police Chief Tom Jackson said he'd planned to release the officer's name Tuesday but changed course after death threats were called into the police department and City Hall, and posted on social media. Jackson said it could be weeks before he releases the name.
"If we come out and say, 'it was this officer,' then he immediately becomes a target," Jackson said. "We're taking the threats seriously."
The race of the officer also hasn't been disclosed, but witnesses said he was white. Brown was black.
Nearly three dozen people were arrested following a candlelight vigil Sunday after crowds burned stores, vandalized vehicles, assaulted reporters and taunted officers. On Monday, there was no looting but officers arrested at least five people and used tear gas and "beanbag rounds" on a large, rowdy crowd at a burned-out convenience store after rocks were thrown at police, investigators said.
"People are tired. They have reached the end of their rope," Ruth Latchison Nichols said after an NAACP-hosted town meeting Monday night that drew hundreds of people. "Enough is enough. This is a state of emergency."
The streets were calm by early Tuesday. A handful of police officers were sitting in patrol cars near the burned-out gas station, vastly outnumbered by news crews.
One shooting witness, Phillip Walker, told The Associated Press he was on the porch of an apartment complex overlooking the scene when he saw a white officer with Brown, who was "giving up in the sense of raising his arms and being subdued."
Walker said the officer "had his gun raised and started shooting the individual in the chest multiple times." He said the officer then "stood over him and shot him."
Dorian Johnson offered a similar account, telling local media that he and Brown were walking home when a police officer told them to get out of the street and onto the sidewalk. Johnson said they kept walking, which caused the officer to confront them and eventually fire his weapon.
"He shot again, and once my friend felt that shot, he turned around and put his hands in the air, and he started to get down. But the officer still approached with his weapon drawn and fired several more shots," Johnson said.
Police have said there was no security or police video of the incident.
The family's attorney, Benjamin Crump, has asked individuals with video of the shooting to come forward. Crump also represented relatives of Trayvon Martin, the 17-year-old fatally shot by a Florida neighborhood watch organizer who was later acquitted of murder charges.
"I don't want to sugarcoat it," he said Monday. "(Brown) was executed in broad daylight."
St. Louis County police are leading the investigation, and the Federal Aviation Administration agreed to order flight restrictions over Ferguson to give police helicopters unfettered access to that air space. The FAA said the action, effective until Monday, wouldn't delay traffic at nearby Lambert-St. Louis International Airport.