The United States rejected an extradition request for the wife of an intelligence officer accused of causing the death of the teenage motorcyclist Harry Dunn.
Dunn, 19, died after an accident in Northamptonshire in August that led the suspect, Anne Sacoolas, to the United States under diplomatic immunity.
The Ministry of Interior initiated extradition procedures earlier this month.
A spokeswoman said the US decision “seems to be a denial of justice.”
Washington, however, said granting the request “would make the invocation of diplomatic immunity a practical nullity.”
US Secretary of State Mike Pompeo rejected the extradition request in an email to the UK government Thursday night, Dunn family spokesman Radd Seiger said.
Seiger said the family would react fully to the news on Friday morning and added that “the struggle continues” for justice for his son.
The family parliamentarian, Deputy Andrea Leadsom, will meet Friday with US Ambassador Woody Johnson in London to discuss the case.
When the Home Office began extradition proceedings, the US Department of State said the request would be “highly inappropriate.”
He insisted that the state of Sacoolas at the time of the accident meant that he had diplomatic immunity.
Prime Minister Boris Johnson said earlier that the possibility that Ms. Sacoolas, accused of causing death by driving dangerously, would return to the United Kingdom was very low.
Dunn died after his motorcycle crashed into a car owned by Mrs. Sacoolas.
The accident happened outside the RAF Croughton, where Mrs. Sacoolas’s husband, Jonathan, worked as an intelligence officer.
The 42-year-old woman left the United Kingdom and returned to her home country, the United States, claiming diplomatic immunity.
In a statement issued on behalf of the suspect after she was charged in December, Ms. Sacoolas’s lawyers said: “Anne will not voluntarily return to the United Kingdom to face a possible jail sentence for what was a terrible but involuntary accident “.
Mr. Seiger said that Mr. Pompeo gave no reason to reject the extradition request.
He also said the family was waiting for the decision, adding: “We knew this day would come. It is not a surprise.”
However, he said the family would continue his campaign and that the extradition request “is there forever.”
“I can assure you that Anne Sacoolas will return one day,” he said. “This is far from over.”
The Interior Ministry said it was “disappointed with this decision that seems to be a denial of justice.”
“We are urgently considering our options,” a spokeswoman added.
A statement from the United States Department of State said: “At the time the accident occurred, and during the duration of their stay in the United Kingdom, the US citizen driver in this case had immunity from criminal jurisdiction.
“If the United States granted the request for extradition from the United Kingdom, it would make the invocation of diplomatic immunity a practical nullity and set an extraordinarily worrying precedent.”