In a historic move sure to be watched nationwide, three current or former Chicago Police officers are facing criminal charges in an alleged cover-up to protect Officer Jason Van Dyke, who fatally shot 17-year-old Laquan McDonald.

Special prosecutor Patricia Brown Holmes on Tuesday announced a three-count grand jury indictment charging patrol officers Joseph Walsh and Thomas Gaffney and detective David March with conspiracy, obstruction of justice and official misconduct.

Holmes accused the trio of allegedly filing false accounts of the October 2014 shooting to keep Van Dyke from being accused of any wrongdoing. She also said the three failed to interview witnesses who might have contradicted their faulty version of events.

March, 58, the lead detective in the McDonald case, cleared Van Dyke of wrongdoing, despite dashcam video that appears to show McDonald walking away from Van Dyke when he opened fire and shot the teen 16 times.

Van Dyke was charged with first-degree murder in November 2015 on the day before that video was publicly released.

“This indictment alleges that these defendants lied about what occurred during a police-involved shooting in order to prevent independent criminal investigators from learning the truth,” Holmes said at a press conference. “The indictment makes clear that it is unacceptable to obey an unofficial code of silence.”

The 11-page indictment lays out a conspiracy by March; Walsh, 48, who was Van Dyke’s partner, and Thomas Gaffney, 43, an officer who was one of the first to encounter McDonald the night of October 21, 2014. The indictment refers to Van Dyke as “Individual A,” and also includes other officers, identified as unidentified individuals “B” through “G.”

Questioned by reporters about the prospect of more officers facing charges, Holmes said repeatedly: “The investigation is ongoing.”

Gaffney — who had been on desk duty and was the only one of the three officers charged who had not retired or resigned — was suspended Tuesday after the charges were announced, police spokesman Anthony Guglielmi said.

Officials from the Fraternal Order of Police Lodge 7, which represents nearly all the department’s rank-and-file police officers, issued a statement saying they will not comment on the ongoing investigation. “At this time, we have not reviewed the indictment and, as general practice, we do not comment on ongoing investigations,” the statement read.

Holmes, a former Cook County judge and federal prosecutor, was appointed special prosecutor 10 months ago at the urging of activists concerned that the criminal investigation of the McDonald shooting would begin and end with the charges against Van Dyke. Joseph McMahon, the Kane County State’s Attorney, has been appointed special prosecutor to handle the murder case against Van Dyke.

Background: The Laquan McDonald story so far

Related: Lawyers, activists agree: Jason Van Dyke guilty verdict no sure thing

The indictment marks the first time CPD officers have been targeted criminally for following an unwritten “code of silence” and for lying to cover for an officer who committed alleged on-the-job misconduct, said Craig Futterman, a University of Chicago Law School professor who was part of the effort to have a special prosecutor probe the handling of the McDonald investigation.

“This is at least as important as prosecuting the individual officer in the fatal shooting for murder,” Futterman said. “If we want that culture (of silence) to end, and police officers want it to end, we have to know that there are consequences when officers lie.”

March, the detective, resigned in August after a city of Chicago Inspector General’s report said the veteran detective should be fired for his handling of the case. The same report also called for firing Walsh, Van Dyke’s partner, who told investigators that McDonald had been moving toward him and Van Dyke and was preparing to throw a knife at them when Van Dyke opened fire.

Cited in the indictment were entries in reports filed by March and other officers that depicted McDonald as moving toward the officers with his armed raised — and that the teen attempted to get up after he was shot. The indictment notes that March viewed the video and wrote in one report that the images were “consistent with the accounts of all witnesses.”

The indictment also notes that the officers did not make an effort to locate witnesses whose accounts of the shooting didn’t match the official version in police reports.

Gaffney was one of the first officers to encounter McDonald on the night of Oct. 21, 2014, in response to a Southwest Side merchant’s report that the teen was breaking into vehicles in a parking lot. The indictment alleges Gaffney submitted reports that stated Van Dyke and other officers had been injured by McDonald in the confrontation.

It is not clear from the indictment how Gaffney’s actions differed significantly from that of the five other officers who were at the scene and gave accounts of the shooting that matched the versions given by Van Dyke and Walsh. Three other officers at the scene said they were looking away or didn’t see the shooting.

It also wasn’t clear how the charges would impact Van Dyke’s murder case. The judge in Van Dyke’s case earlier this month had said he wanted March to testify about statements Van Dyke made at the shooting scene.

A spokesman for Holmes said Tuesday that members of special prosecutor’s unit are not allowed to follow developments in Van Dyke’s case and that the timing of the indictment had nothing to do with March’s planned upcoming testimony.

Under an agreement with prosecutors, the three officers will make their first appearance in court on the charges on July 10, where they will be arraigned and bond will be set. The charges all are felony counts that carry sentences of up to 6 years in prison.