Here’s a question for US Attorney-General William Barr: why has the FBI, which falls under your purview, sat for nearly 16 months on the unwarranted killing of an unarmed young accountant shot to death by US Park police officers just outside Washington?

The accountant was Bijan Ghaisar, who exercised bad judgment, but committed no serious crime, when he drove off after his car was rear-ended in a fender bender on the George Washington Parkway in November 2017.

In a sequence then caught on a police cruiser’s dash-cam video, he twice drove away after being pulled over by two Park police officers who approached his vehicle with guns drawn. When he seemed to try to do so a third time, they fired nine shots into his car; he died a few days later.

Three days after the shooting, the FBI took over the investigation. Since then, not a jot of information has been made public, for month after month after month. Among the basic questions that have gone unanswered, and to which Barr should seek answers, are:

• Why have the identities of the Park police officers not been disclosed?

• Why did they violate standard police practice, first by giving chase after a minor accident and second by drawing their guns when approaching Ghaisar’s car?

• Why did they open fire on Ghaisar, who was unarmed and, judging from video evidence, posed no threat?

Given the existence of clear dash-cam video, recorded by a Fairfax County, Virginia, police car that tailed the Park police, why would the FBI go nearly 16 months without presenting any investigative conclusions either to the Ghaisar family or to the public?

Why has FBI Director Christopher Wray ignored a letter sent in December by Charles Grassley, the senator from Iowa, who was then the chairman of the Senate Judiciary Committee, seeking information on the status of the investigation? Why have FBI officials disregarded a half-dozen follow-up attempts by Grassley’s staff?

Why has Wray similarly ignored a request to meet from Don Beyer, the representative from Virginia, in whose district the shooting occurred?

As Grassley said in his letter to Wray, investigations into deadly police shootings “should be handled in a manner that reinforces public confidence in law enforcement”. The FBI’s almost 16-month silence in the Ghaisar investigation does the opposite. It subverts public confidence and generates suspicions that the agency, and possibly Park police, are engaged in a cover-up.

Grassley’s letter to Wray was a straightforward request for information: had the FBI completed its investigation? If not, when would it be complete, and would an update be provided in the meantime to the Senate Judiciary Committee? Further, the senator asked whether the agency would commit to providing the committee with a copy of the final investigative report. He asked that the FBI director respond by December 28.

The FBI’s conduct in the Ghaisar investigation is a case study in stonewalling, arrogance and non-accountability. Barr should act immediately to address it.