St. Louis County police have so far interviewed 12 people from the Ferguson, Mo. community for information about the shooting death of Michael Brown, not counting officers, a police spokesman said Wednesday afternoon.

Several officers have also been interviewed by authorities, the spokesman said.

News of the investigation’s progress comes as frustration mounts nationwide about the lack of a clear account from police of how the unarmed 18-year-old ended up being shot multiple times and killed by a Ferguson police officer Saturday afternoon. According to witnesses, Brown was shot without threatening the officer in any way; in the police account, Brown struggled with an officer over his weapon and in his car.

Investigators at the county police department, which took over the investigation from the small borough within a day of the incident, said on Wednesday morning that they have not yet interviewed a key firsthand witness, Dorian Johnson. He is a friend of Brown’s and says he was walking with him when they were approached by police that evening.

Johnson has told reporters an account in stark contrast to the police description of the shooting. Johnson says a Ferguson police officer approached him and Brown when they were just blocks from home, ordering them both to get off the street, and shooting Brown when he came forward with his hands up in the air.

County Police Sgt. Colby Dolly said police have made every effort to hear Johnson’s account firsthand.

“We have reached out to numerous people in his network, family and friends, and are doing everything we can to talk to him,” Dolly said. “There is an open invitation for him to be interviewed.”

Johnson has said he fears police retaliation. An attorney for Johnson told The Post that he would be speaking with the FBI, which is also investigating the shooting, as well as the county prosecutor on Wednesday.

Dolly added that many more witnesses will likely be interviewed: “The prosecuting attorney would like anyone to come forward, whether their evidence is favorable or unfavorable to the police. “

Wesley Lowery in Ferguson, Mo., contributed to this report.