Police say Ms. Sacoolas was driving 60 miles an hour the wrong way down a street on August 27 when she collided with teenager Harry Dunn on his motorcycle, killing him, according to The New York Times.
According to the 1961 Vienna Convention on Diplomatic Relations, foreign diplomats and their family members are given certain protections that allow them to avoid arrest for nearly any crime unless the diplomat's home country decides to waive immunity.
USA diplomat's wife Anne Sacoolas is a suspect in inquiries into the death of motorcyclist Harry Dunn.
Britain's Prime Minister Boris Johnson says he hopes that Anne Sacoolas will return to Britain to face justice.
The teenager with his mother Charlotte Charles, who said that her family have been denied the opportunity to grieve. We're a usual United Kingdom family that just need to put a face to what we have now as a name.
"We don't wish her any harm".
"The next minute we found out that actually, she and her family had left, so it is really disappointing, which prompted the letter from me to say we want to see justice done and the family have a right to see justice done", he said.
Family members of diplomats are covered under the 1961 Vienna Convention on Diplomatic Relations.
The mother of a British teenager who was killed in a auto crash, allegedly by the wife of a U.S. diplomat, has said the death of her son has destroyed her family.
United States authorities declined Northamptonshire police's request to waive diplomatic immunity of 42 year-old Sacoolas soon after the incident.
Mr Dunn, from Banbury in Oxfordshire, was hit by an Volvo SUV believed to have been driven by Anne Sacoolas, 42, whose husband Jonathan worked at RAF Croughton for the USA government.
"The Prime Minister offers his condolences to the family". The case will receive intense attention at senior levels, the spokesperson said, and the department will consider its global impact, as it does with all cases like this. The victim was 19-year-old Harry Dunn.
A fundraising page that was created to help the family with their quest for justice has attracted hundreds of donations, with more than £6955 ($13,600) raised so far.
"The loss of Harry is going to leave the biggest hole in our lives and he will truly be missed by all."
Harry's parents have previously said that they want her to apologise face-to-face.
Johnson stood up for the family of 19-year-old motorcyclist Harry Dunn on Monday, telling reporters that Anne Sacoolas' claim of diplomatic immunity is unjustified. This means that they can avoid arrest for nearly any crime in another country, although the home country is allowed to waive immunity, WaPo reported.
"He was working at Croughton, which is a communications base, so he was working with intelligence which is, I guess, why it has been handled in the way that it has", said Radd Seiger.
"Unfortunately we were latterly advised that the waiver had been declined and the suspect had left the UK", Northamptonshire Police Superintendent Sarah Johnson told Sky News television. "I'm angry that someone could do this and then get on a plane and go".
The PM added: "I hope it will be resolved very shortly".