FERGUSON, Mo. — The FBI said Monday it had opened an inquiry into the weekend shooting death of an unarmed black teenager by a police officer that sparked a second night of unrest in Ferguson, a suburb of St. Louis.
Special Agent Cheryl Mimura, of the FBI’s office in St. Louis, said the agency had begun an investigation into possible civil rights violations connected to the death of Michael Brown, 18, who had been planning to begin college classes Monday.
The circumstances of Brown’s death remained in sharp dispute two days after he was killed by a police officer in Ferguson, a city of about 21,000 northwest of St. Louis. Police have said an officer, who has not been identified, was “physically assaulted” before opening fire early Saturday afternoon. Authorities also said there had been a struggle “over the officer’s weapon.”
But critics have questioned the police account and demanded that the officer face prosecution.
On Monday, Chief Jon Belmar of the St. Louis County Police Department said an autopsy had shown that Brown had been “struck several times by gunfire.”
Two witnesses said Brown had his hands raised when the officer approached him with his weapon drawn and fired repeatedly.
Phillip Walker said he was on the porch of an apartment complex overlooking the scene when he heard a shot and saw a white officer with Brown on the street.
Brown ‘‘was giving up in the sense of raising his arms and being subdued,’’ Walker said Monday. The officer ‘‘had his gun raised and started shooting the individual in the chest multiple times.’’ The officer then ‘‘stood over him and shot him’’ after the victim fell wounded.
Dorian Johnson offered a similar account when he told KMOV-TV that he and Brown were walking home from a convenience store 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 from his car and again after getting out of his car.
Johnson said the first time the officer fired, he and Brown got scared and ran away.
‘‘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,’’ Johnson said. ‘‘But the officer still approached with his weapon drawn and fired several more shots.’’
‘‘We wasn’t causing harm to nobody,’’ Johnson said. ‘‘We had no weapons on us at all.’’
Walker acknowledged that he did not see a scuffle or the circumstances surrounding the first gunshot.
The police department refused to discuss Johnson’s remarks, citing the ongoing investigation.
But Belmar previously said that the officer encountered Brown and another man outside an apartment complex and that one of the men pushed the officer into his squad car and they struggled over the officer’s weapon.
Belmar’s agency has been leading the investigation, and Mimura said the county police would continue their work as the FBI conducted its review.
At a news conference Monday, Belmar pleaded for the public’s patience.
“I understand that the public has a right to be skeptical, and I appreciate that and I would expect that the public be skeptical oftentimes of government or some forms of it,” he said. “But I would also ask the public to be reasonable because it takes a long time to make sure we do this investigation the right way.”
On Monday night, authorities in Ferguson used tear gas and rubber bullets to try to disperse a large crowd that had gathered at the site of a burned-out convenience store damaged a night earlier, when many businesses in the area were looted.
Police Chief Tom Jackson said members of the crowd threw rocks at police and gunfire came from the crowd, so officers used tear gas and shot ‘‘beanbag rounds’’ meant to stun them.
An Associated Press photographer said police were telling people to go home, but authorities had blocked exit streets off. Jackson said police blocked off the area where most of the looting and vandalism occurred the previous night out of concern that cars passing by might hit demonstrators in the street.
After a vigil Sunday for Brown, protesters took to the streets, looting stores, vandalizing cars, and confronting police. Crowds flooded the streets near the scene of the shooting, some of them chanting “No justice, no peace.”