LONDON — U.S. citizen Anne Sacoolas, 45, who according to her lawyers was working for a U.S. intelligence agency, pleaded guilty Thursday in British court to causing death by careless driving, when she drove on the wrong side of the road and killed a 19-year-old motorcyclist.

The plea marked a step forward in what has become a high-level diplomatic dispute and three-year fight for justice by the family of the victim, Harry Dunn. Sacoolas’s sentencing is scheduled for November.

The case is unique because the U.S. government asserted that Sacoolas, who was a State Department employee, had diplomatic immunity following the crash, and she left Britain less than three weeks after the incident while the investigation was ongoing.

It is also rare in Britain for a defendant to appear for an entire criminal case via video link, as Sacoolas has so far. The judge in the case ordered Sacoolas to appear in person for her sentencing — but it is unclear if she will.

She could be sentenced to a relatively short prison sentence — with a maximum of five years — but shorter sentences and community service are also possible.

Dunn’s mother, Charlotte Charles, told reporters after the guilty plea that it represented the fulfillment of a promise that she made the night her son was killed, and that she can “stand aside now and let the courts do their thing.”

“Every single day, every bit of pain that you feel from the minute you wake up to the minute you go to bed - all of the hours that you lay awake at night, fighting that pain and keeping it in the pit of your stomach, which kept the promise burning as well,” she said. “It was like it was just all released.”

In court hearings in Britain and the United States, Sacoolas has been described as the wife of a U.S. intelligence officer and as an intelligence officer herself.

At the U.S. District Court in Alexandria, Va., in 2021, one of her lawyers, John McGavin, said, “Mr. and Mrs. Sacoolas were employed by an intelligence agency of the United States, and that’s why she left.”

McGavin told the court that he was unable to “completely candidly” explain the family’s departure. “I know the answer, but I cannot disclose it,” he told the court.

Sacoolas had diplomatic immunity asserted on her behalf by the U.S. government following the crash near an air force base in Northamptonshire, England — and was able to leave Britain 19 days after the incident.

The U.S. government refused to extradite Sacoolas to Britain to face charges in person.

Since the fatal crash, Dunn’s family has campaigned for Sacoolas to be stripped of her diplomatic immunity so that she could return to face the courts.

Dunn was killed in August 2019 when Sacoolas struck his motorcycle while she was driving on the wrong side, according to British police.

Sacoolas was merging onto a roadway near Royal Air Force Croughton station, a U.S. Air Force installation, where many intelligence workers are based. Sacoolas, her diplomat husband and her children had recently moved to the base.

She had been in Britain only a short time, and as newcomers quickly learn, the British drive on the left side of the road, while Americans drive on the right.

She had been formally charged with “causing death by dangerous driving” in 2019, but admitted guilt to a lesser charge of death caused by “careless driving” — a guilty plea accepted by the Crown Prosecution Service, which conducts criminal prosecutions in England.

Then-Prime Minister Boris Johnson said in June 2021 that he and President Biden were “actively engaged” on the case of Dunn.

The Dunn family reached a settlement in a U.S. civil suit against Sacoolas in 2021. Dunn’s parents had launched a U.S. federal lawsuit claiming wrongful death. In September 2021, the family’s spokesman, Radd Seiger, told The Washington Post that the civil case was “resolved,” and they could move on to the criminal case.