She added that no evidence surfaced that Ms. A ever had personal contact with Oakland police Officer Brendan O'Brien, who reportedly mentioned being involved with the teenager in a suicide note found after he took his own life a year ago.

O'Malley said charges are being filed against:

Ricardo Perez, Contra Costa County Sheriff's Office (resigned): one count of oral copulation with a minor (felony) and one count of engaging in a lewd act in a public place (misdemeanor).

Dan Black, Livermore Police Department (resigned): two counts of engaging in an act of prostitution, two counts of engaging in lewd acts in a public place (all misdemeanors).

Brian Bunton, Oakland Police Department: one count of obstruction of justice (felony) and one count of engaging in an act of prostitution (misdemeanor).

Terryl Smith, Oakland Police Department (resigned): Four counts of unauthorized access to a criminal justice computer system (misdemeanors). O'Malley said investigators believe Smith had sexual contact with Ms. A in Contra Costa County, which is outside her office's jurisdiction. Earlier this year, Contra Costa County authorities declined to bring charges against Smith.

Warit Utappa: One count of unauthorized access to a criminal justice computer system (misdemeanor). O'Malley said investigators believe Smith had sexual contact with Ms. A in Contra Costa County, which is outside her office's jurisdiction.

Leroy Johnson, Oakland Police Department (retired): One count of failing to report sexual misconduct involving a minor.

Giovani LoVerde, Oakland Police Department: One count of oral copulation with a minor (felony).

In a series of interviews with police investigators and in media interviews, Ms. A had alleged having sexual contact with 30 or more officers. News accounts included text messages between Ms. A and men identified as police officers. Many Bay Area law enforcement officers had become her friends on Facebook -- including at least two dozen from San Francisco.

But O'Malley said the available evidence, obtained in interviews with Ms. A and other witnesses as well as from the voluminous social media and electronic records, failed to support charges against more officers.

"We determined that the extrinsic evidence contradicts or sheds reasonable doubt on allegations of criminal conduct, such as serious inconsistencies in the statements taken from the witness or contradictions between the witness's statements and the social media messaging," O'Malley said.

O'Malley also emphasized the victim's participation will be crucial to the prosecution of the charged officers.

The Richmond Police Department -- one of the law enforcement agencies whose officers have been accused of involvement with Ms. A -- arranged to send her to a rehab facility in Florida last month. She's now in jail there facing battery charges stemming from an altercation at the treatment facility.

O'Malley criticized Richmond officials for failing to notify her office of its plans to send the key witness in the case out of state, especially when she could have been treated someplace in the Bay Area.

"We were not consulted," she said. "We were not informed. And we protested once we learned she had been moved. We are now working to get Ms. A back here. And if the agency that sent her to Florida does not pay for her to come back, we will pay her airfare to come back to the state."

Earlier this week, Oakland officials announced they're moving to fire four officers and discipline seven others in connection with the case.

The allegations that dozens of officers in Oakland and elsewhere had exploited a teenager working in the sex trade triggered a period of unprecedented turmoil in a department that has had more than its share of scandals and embarrassments in the last couple of decades.

Police Chief Sean Whent’s handling of the case is believed to have led directly to his abrupt resignation in June, a move that was followed by the appointment and departure of two interim chiefs within an eight-day span. The Police Department is currently under the control of City Administrator Sabrina Landreth until the city hires a permanent chief.

This is a breaking story and will be updated.