The fatal accident occurred on a roadway in the village of Croughton, England, on the night of Aug. 27, when a black Volvo XC90 collided head-on with a black Kawasaki motorcycle traveling in the opposite direction. The rider of the motorcycle, 19-year-old Harry Dunn, was taken to a hospital in the nearby city of Oxford, where he died soon after, according to press releases from Northamptonshire Police.
The crash scene was less than a mile down the road from Royal Air Force Croughton, commonly known as RAF Croughton, which is a British military station that houses an intelligence-gathering base operated by the United States Air Force.
Over the weekend, Northamptonshire Police superintendent Sarah Johnson revealed that a 42-year-old American woman who is "being treated as a suspect" in the investigation has left the nation after allegedly telling investigators she had no plans to do so. Police intended to arrest and formally interview the woman, who has not been officially named.
"Northamptonshire Police followed all of its usual procedures following the incident, including liaising closely with the suspect, who engaged fully with us at the time and had previously confirmed to us that she had no plans to leave the country in the near future," Johnson said in a statement Saturday. "Due process was also followed in seeking the necessary documentation to allow for the arrest and formal interview of the suspect, and the force is now exploring all opportunities through diplomatic channels to ensure that the investigation continues to progress."
Northamptonshire Police are also "working closely" with the U.K. Foreign and Commonwealth Office "in an effort to come to a resolution regarding this matter," according to Johnson.
“Harry Dunn’s family deserve justice," she added, "and in order to achieve this, a full and thorough investigation, with the assistance of all parties involved, needs to take place."
While offering "our deepest sympathies" to Dunn's family, a spokesperson for the U.S. Department of State confirmed that the Aug. 27 incident involved "a vehicle driven by the spouse of a U.S. diplomat assigned to the United Kingdom." The U.S. government is in "close consultation with the appropriate British officials," the spokesperson told ABC News in a statement Saturday.
"Any questions regarding a waiver of immunity with regard to our diplomats and their family members overseas in a case like this receive intense attention at senior levels and are considered carefully given the global impact such decisions carry," the spokesperson said. "Immunity is rarely waived."
British media outlets reported that the woman left the United Kingdom after claiming diplomatic immunity, which protects diplomats and their family members from prosecution or lawsuits under the host country's laws.
British Foreign Secretary Dominic Raab said in a statement Saturday that he has called the U.S. Ambassador to express his "disappointment." Raab also spoke with U.S. Secretary of State Mike Pompeo on Monday to talk about a range of issues, including "the case of Harry Dunn where he reiterated his disappointment with the U.S. decision and urged them to reconsider," according to a spokesperson for the U.K. Foreign and Commonwealth Office.
Pompeo's spokesperson, Morgan Ortagus, confirmed in a statement Monday that the two discussed "the tragic death of a British citizen in an accident involving the spouse of an American diplomat."
During an interview with Sky News on Monday, Dunn's parents said police have surveillance video purportedly showing the woman pulling out of RAF Croughton and driving on the wrong side of the road for some 400 yards before hitting their son.
"She has left a family in complete ruin," Dunn's mother, Charlotte Charles, told Sky News. "We are just utterly shocked and appalled that somebody can just get on a plane and go home and avoid our justice system."
Dunn's parents said they don't necessarily want the woman to be punished for fleeing the nation, but do want an opportunity to speak with her in person so they can begin to have some sense of closure over their son's untimely death.
"It's not much to ask," the mother told Sky News.
While speaking to reporters Monday, British Prime Minister Boris Johnson identified the American diplomat's wife as Anne Sacoolas. He called Dunn's death a "tragic loss" and said he will personally raise the issue with U.S. President Donald Trump if Sacoolas does not return soon to face the U.K. investigation.
"I do not think that it can be right to use the process of diplomatic immunity for this type of purpose," Johnson told reporters.
ABC News' Guy Davies, Conor Finnegan and Joshua Hoyos contributed to this report.