FERGUSON, Mo. — Missouri Gov. Jay Nixon declared a midnight-to-5 a.m. curfew Saturday in the city of Ferguson after fresh violence erupted overnight amid public anger over the shooting death of an unarmed young black man by a white police officer.

At a chaotic news conference where Nixon was shouted down at times by residents demanding charges be filed against the policeman, the governor said the only way to restore peace was by ensuring safety on the streets.

“We cannot have looting and crimes at night,” Nixon said, referring to the latest spate of violence that left three businesses with shattered windows and looted shelves. “We can’t have people fearful.”

At that, someone in the crowd yelled: “We can’t have police officers killing people!”

Missouri Highway Patrol Capt. Ron Johnson, whom Nixon put in charge of Ferguson’s security on Thursday, said enforcement of the curfew would not be heavy-handed.

“We won’t enforce it with tear gas. We won’t enforce it with trucks,” Johnson said, a reference to the militaristic response protesters faced in the nights after Michael Brown’s death a week ago.

Brown, who was 18, was shot and killed Aug. 9 by Darren Wilson, a six-year police veteran with no previous disciplinary issues. Police say Wilson shot Brown when the young man attacked him. Witnesses say that Wilson was the aggressor and that Brown was holding his hands in the air at the time he was shot.

The circumstances of the shooting and the initial secrecy surrounding the police officer’s role and identity-it took Ferguson’s police chief six days to name Wilson-infuriated Brown’s family, many Ferguson residents and civil rights activists.

Johnson, who is black and grew up in Ferguson, was seen as a salve when he took over security from Ferguson Police Chief Thomas Jackson, who is white. Ferguson enjoyed one night of calm Thursday after Johnson’s appointment.

But that changed Friday after Jackson released a police report identifying Brown as a suspect in a strong-arm robbery.

 that occurred minutes before Brown’s encounter with Wilson. Critics lashed out at Jackson, accusing him of trying to deflect attention from what they say was the true crime: Wilson’s shooting of Brown.

FBI agents have begun interviewing people in Ferguson as part of a federal investigation into the shooting. St. Louis County prosecutors also are investigating Brown’s death, but there have been calls for the county prosecutor, Robert McCulloch, to withdraw from the inquiry because of what some critics say is a poor history of prosecuting law enforcement officers in controversial cases.

“I would feel more comfortable with a higher authority” doing the investigation, said U.S. Rep. William Lacy Clay, a Democrat. Speaking in a telephone interview Saturday, Clay said that the “only way to reach justice” was to go outside the county because of the “past history of prosecutions of police shootings in St. Louis County.”

“There is a history of reduced charges or no convictions at all,” said Clay.

Missouri state Sen. Jamilah Nasheed, another Democrat, agreed. “They don’t believe he can be fair and impartial,” she said on CNN, regarding community reaction toward McCulloch.

Ed Magee, spokesman for the county prosecutor’s office, said McCulloch was moving to present evidence to the grand jury as soon as the coming week. Magee discounted the criticism about the prosecutor’s objectivity.

“That’s just not true. He can be objective,” Magee said, noting that McCulloch has held the elected office since 1991. “Always has been.”

In 2000, McCulloch was in office when two white law enforcement officers shot to death two unarmed black men in a car in Berkeley, about two miles from Ferguson. Then, as now, officials delayed identifying the officers amid public anger.

A grand jury declined to indict the officers, who said they feared being run over as they tried to arrest one of the men in the car whom they suspected of a drug crime. But a federal civil rights investigation concluded that the officers fired “out of fear and panic.” The St. Louis Post-Dispatch reported that grand jury tapes showed that only three of 13 detectives who testified said the men’s car was moving toward the police when the officers opened fire. Two of those three were the shooters.

Clay said the release of the police report naming Brown as a robbery suspect, and the police department’s release of a video of the purported robbery, underscored the need for an outside investigation.

A federal law enforcement source said Saturday that Ferguson police planned to release the video Thursday, but were talked out of it by federal officials.

“We strongly objected and we told them it would just embroil the community,” the source said. Federal officials were surprised when the local police went ahead and released the video Friday.

“The federal government was fearful the release of those photos would incite more violence-which it did,” Clay said.

Many in the community said the video ignited a new round of anger in Ferguson-but also a fierce desire by many residents to stop the attacks on local businesses.