Video report by ITV News Correspondent Richard Pallot
The parents of a teenager killed in a road crash say they are "trapped in a living nightmare" after the suspect in his death - a US citizen - claimed diplomatic immunity and fled the country.
Harry Dunn died when his motorbike was involved in a crash with a car near RAF Croughton in Northamptonshire.
The 19-year-old's parents have said they will do everything they can, even travelling to the US, to get "justice" for their "big-hearted" and "fun-loving" son.
The US Embassy confirmed the incident involved “a vehicle driven by the spouse of a US diplomat assigned to the United Kingdom” and that the family has left the UK.
The 42-year-old was questioned by police in the aftermath of the crash - which happened on August 27 - but said she had no plans to leave the country.
British appeals for the woman's immunity to be removed have so far been rejected, with American officials warning “immunity is rarely waived”.
According to the Vienna Convention on Diplomatic Relations, families of diplomats are granted immunity from arrest.
However, the sending state is able to issue a waiver of immunity.
Tim Dunn, Mr Dunn's father said it felt as if his "heart had dropped out" when he learnt, a week after his son's funeral, that the woman who was suspected of involvement in the crash had left the country
"It was like all hope had gone," the teenager's mother, Charlotte Charles added.
"It was literally a living nightmare.
"We were desperate to wake up in the morning and hope to God that it wasn't true."
Ms Charles added that she and Mr Dunn's father will be meeting with Foreign Secretary Dominic Raab in the coming days and hope he can "help us get her back and tell us the truth".
"We're not going to be swept under the carpet," she added.
"Harry always fought for what he believed in... we're going to carry on that."
Speaking on Sky News, Housing Secretary Robert Jenrick said Mr Dunn's family "have our [the Government's] absolute assurance that we're going to do everything we can to resolve this.
"We want the police to be able to continue their enquiries, and for whatever actions they deem fit to be able to take place and for justice to be done."
Mr Dunn's parents called on US President Donald Trump to "do the honourable thing, take away the immunity" to allow the suspect to "come back.
"We need her to face the consequences."
They added they were prepared to "take this all the way if we have to."
Mr Dunn's father said the pair "could not let our son die and then nothing be answered for".
"We'll go as far as we need to go," Ms Charles added, "to get justice for our boy and to do our best to stop another family suffering".
Ms Charles added that the lifting of diplomatic immunity would "ease" their "pain to some degree" as Mr Dunn's parents "can't even begin to grieve properly... we haven't begun yet, we're angry... there's absolutely no closure... for us the funeral was just the beginning....
"We've got a long way to go, but we're going to do our best."
In a statement, a spokesperson for the US Embassy 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.”
Foreign Secretary Dominic Raab has spoken to the US ambassador to ask the embassy to “reconsider” its decision.
In a statement, Mr 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."