The FBI agents who investigated the fatal shooting of unarmed motorist Bijan Ghaisar in 2017 will not be allowed to testify in front of a Fairfax County grand jury if Fairfax prosecutors decide to pursue charges against the two Park Police officers who killed Ghaisar.

The head of the Justice Department’s Civil Rights Division informed Fairfax prosecutors that the department was considering defending the officers in a lawsuit filed by Ghaisar’s family, and if it did, that would create a conflict of interest, according to letters released Friday. Assistant Attorney General Eric S. Dreiband added that the Justice Department believes that “a federal officer may not be prosecuted by a State for actions undertaken in the course of performing the officer’s official duties,” when the officer’s actions are “objectively reasonable,” according to legal precedents.

The decision tosses another obstacle in the path of the Ghaisar family’s arduous pursuit of justice, which has seen a two-year wait for a decision on federal criminal charges, and a lawsuit that has languished in federal court in Alexandria for 18 months.

Roy L. Austin Jr., one of the Ghaisar family’s lawyers, said Dreiband’s letter “is clearly meant as a warning to Fairfax County and all other local prosecutors to not prosecute federal officers, no matter how egregious the conduct. Hopefully, Fairfax County is steadfast in its apparent desire to conduct a fair and thorough investigation, and where appropriate, seek justice for those impacted by unlawful police violence.”

Steve Descano, the top Fairfax County prosecutor, said in a response to Dreiband that he would continue to pursue the investigation “as well as continue to request and expect the Department’s future cooperation when necessary.” Descano released both the Dreiband letter and his response Friday morning.

The Justice Department decided in November not to file federal criminal civil rights charges against Officers Lucas Vinyard and Alejandro Amaya, who fired 10 shots into Ghaisar’s Jeep Grand Cherokee as it slowly drove away from them on Nov. 17, 2017. In announcing that decision, the department said its ruling did not preclude other agencies from pursuing the case.

Then-Fairfax Commonwealth’s Attorney Raymond F. Morrogh promptly stepped in, obtaining the FBI’s files in the case and making plans in December to present the case to a Fairfax grand jury for possible murder charges. But the Justice Department wouldn’t immediately allow the FBI agents to testify, saying the department hadn’t been given enough advance notice.

Morrogh stepped down Jan. 1, and his successor, Descano, said he would continue to investigate the case, and waited for the Justice Department’s decision on whether to allow the agents to testify. In a letter dated Feb. 6, Dreiband said the Interior Department had asked the DOJ to represent Vinyard and Amaya in the lawsuit, and the Civil Rights Division has not decided whether to do so.

“In view of the possibility that the Department may represent the officers,” Dreiband wrote, “the Department is unable to authorize Department employees, including FBI agents, to appear before a state grand jury in Fairfax County.”

The Park Police officers chased Ghaisar’s Jeep after he was involved in a fender bender in Alexandria on the George Washington Memorial Parkway, where Park Police have jurisdiction, and then left the scene. In video recorded by a Fairfax police lieutenant who followed the pursuit, Ghaisar can be seen stopping three times for the police, who then approach him with guns drawn, and then driving away. The third time, Vinyard and Amaya opened fire in three separate bursts, striking Ghaisar four times in the head.

Fairfax police responded to the scene, but they have said that Park Police officials told them they were not needed, the Park Police would investigate the case. Park Police have jurisdiction in Fairfax County under Virginia law. The Fairfax police backed off, other than to investigate their own officers who joined the pursuit, but Fairfax Chief Edwin C. Roessler Jr. did release two videos of the shooting from two in-car Fairfax cruisers.

After three days, the Park Police handed the case off to the FBI. Then-Chief Robert MacLean said this was done to ensure an objective investigation. Dreiband’s letter states that the Justice Department “invited Fairfax County to participate in the Department’s investigation. Fairfax declined to do so.”

Roessler responded, “That is not true. I never declined to assist them.” Roessler said the FBI asked Fairfax police to join the investigation early on, and it was agreed that a Fairfax detective would serve as a liaison to the FBI investigation, providing access to things such as the Fairfax police vehicles which joined the chase. Roessler provided emails from November 2017 including one from a Fairfax commander to the FBI, four days after the shooting, which said, “FCPD will provide support to your efforts in investigating this OIS [officer-involved shooting] which the FBI will present to the United States Attorney for adjudication.” An FBI agent responded, “Thank you and we look forward to working with your office.”

“We never declined,” Roessler said. “They were the lead. We assisted.”

Dreiband’s letter said that after his division declined charges on Vinyard and Amaya, the Justice Department “voluntarily shared its investigative files with the County … Nothing prevents Fairfax County from having its own detectives now review those same case files, conduct their own investigation, and testify before the Fairfax County grand jury.”

It would be highly unusual for a police agency that wasn’t involved in a case to review another agency’s files, and then testify about them before a grand jury. Morrogh decided against it, and subpoenaed the FBI agents on Dec. 13, for testimony on either Dec. 16 or Dec. 18. Officials in the U.S. attorney’s office in Washington responded that they needed more time to review the request, and Morrogh left the case for Descano.

Descano, a former assistant U.S. attorney who handled tax cases, responded to Dreiband by saying that he intended to investigate the case fully, and that Dreiband should let him know if the Justice Department decided not to represent the officers. Vinyard and Amaya have been represented by private attorneys since shortly after the Ghaisars filed suit in August 2018. The lawsuit was delayed for a year when Justice Department lawyers representing the Park Police successfully argued that Ghaisar’s parents had not qualified as their son’s executors when they began legal proceedings.

Amaya, 40, and Vinyard, 38, have been on administrative duty with pay since April 2018, the Park Police said. The Park Police have not begun an internal investigation until all possible criminal proceedings are resolved. It is not known if the officers gave statements to the FBI, which they are not required to do under the Fifth Amendment, and they have not spoken publicly about why they shot Ghaisar.

Upon learning of the Justice Department’s decision, Sen. Mark Warner (D-Va.) issued a statement which said, “I still have a lot of questions about this entire situation, and I am going to continue pressing the Department of Justice for answers. I’m also keeping pressure on the Department of the Interior and the National Park Service, which to date have declined to respond to questions about their use of force policies, or provide any semblance of an explanation to the Ghaisar family for what happened to Bijan. I am appalled that to date, there has not even been an internal affairs investigation into the events that led to an unarmed young man being shot and killed more than two years ago.”

This story has been updated.