The family of a teenager killed in a motorbike accident have appealed for the wife of a US diplomat at the centre of the inquiry into the fatal crash to return to the UK.
Harry Dunn, 19, died after his bike collided with a car near RAF Croughton in Northamptonshire on August 27.
The unidentified woman, the spouse of a US diplomat, has now left the UK after becoming a suspect in the police investigation into the crash.
Northamptonshire police confirmed that a 42-year-old American woman being treated as a suspect in their investigations has left the country.
Superintendent Sarah Johnson said: "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.
ITV News Correspondent David Wood says the situation has the potential to blow up into a full-scale political row
"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.
"We are also working closely with the Foreign & Commonwealth Office in an effort to come to a resolution regarding this matter.
"Harry Dunn's family deserve justice and in order to achieve this, a full and thorough investigation, with the assistance of all parties involved, needs to take place.
"Northamptonshire Police is committed to ensuring justice for Harry and specially trained officers continue to support the Dunn family in their loss, including keeping them fully informed of all developments in the investigation."
Family spokesman Radd Seiger told the PA news agency that Mr Dunn's family were "utterly devastated" and "not coping well at all" following the teenager's death.
He added: "It that weren't bad enough they now have a situation not of their making where the American government has whisked this American citizen back to the US before they could get some justice."
Speaking to Sky News, Mr Dunn's mother Charlotte Charles said: "Everyone loved him, we're utterly broken inside and out, everything hurts day and night, it's an effort to do anything, I ache from it, every limb, every internal organ hurts."
A crowdfunding webpage has been set up to provide support to Mr Dunn's family, including his twin brother Niall.
The gofundme page, that has so far raised just over £1,000, says Mr Dunn was an avid fan of Northampton Town football club whose "love for his family and friends... outshone everything and made him the caring and loving young man he was".
Former world boxing champion Frank Bruno weighed in with his support, tweeting: "The family need closure. No one should be immune to facing justice and left with no proper answers."
In a statement, Foreign Secretary Dominic Raab said: "I wish to offer my condolences to the family affected by this tragic incident.
"I have called the US Ambassador to express the UK's disappointment with their decision, and to urge the Embassy to re-consider it."
Meanwhile, a US embassy spokesman said: "We express our deepest sympathies and offer condolences to the family of the deceased in this tragic traffic accident.
"Any questions regarding a waiver of the 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; immunity is rarely waived.
"The US Embassy has been and will continue to be in close contact with appropriate British officials."