- Video report by ITV News Correspondent Neil Connery
The mother of a teenager who died in a crash involving a US diplomat's wife, has said the family are making "progress" in their efforts to get justice for their son.
Harry Dunn died when his motorbike crashed with a car outside RAF Croughton in Northamptonshire on August 27.
Despite speaking to police at the scene, the suspect, 42-year-old Anne Sacoolas - who is reportedly married to a US intelligence official - was granted diplomatic immunity following the crash and left the country for the US.
Mr Dunn's parents, Charlotte Charles and Tim Dunn, have flown to New York to "put pressure on the US administration to do the right thing".
Speaking on board the flight, Ms Charles told ITV News Correspondent Neil Connery that: "We feel at last we’re starting to make some progress.
"Bit by bit we’re getting there.
"We really hope so.”
They will appear on a major American breakfast show on Monday morning to maximise the pressure on US authorities and get justice for their son.
Ms Sacoolas's lawyer said she is "devastated" by what happened and that she "would like to meet with Mr Dunn's parents so that she can express her deepest sympathies and apologies for this tragic accident".
Mr Dunn's family have also said the Foreign and Commonwealth Office (FCO) has written to them to say Ms Sacoolas does not have diplomatic immunity.
The family's spokesperson, Radd Seiger, said Foreign Secretary Dominic Raab has written to the 19-year-old's family about Ms Sacoolas, saying: "The US have now informed us that they too consider that immunity is no longer pertinent."
The letter, sent by Dominic Raab to the family, said: "We have pressed strongly for a waiver of immunity, so that justice can be done...
"Whilst the US government has steadfastly declined to give that waiver, that is not the end of the matter.
"We have looked at this very carefully... the UK Government's position is that immunity, and therefore any question of waiver, is no longer relevant in Mrs Sacoolas' case, because she has returned home."
Mr Raab added that the matter was now "in the hands" of Northamptonshire Police and the CPS.
Before the letter was sent by the FCO, the family's lawyer Mark Stephens said there are around 20,000 diplomats in the UK, but Ms Sacoolas's husband was not one of them "and therefore was not entitled to diplomatic immunity.
"That has a number of consequences.
"That means that the Americans have made a false claim.
"She would not have been entitled to claim diplomatic immunity."
Mr Seiger said in a statement that he had spoken with Amy Jeffress, Ms Sacoolas's lawyer, and the pair had agreed "to get together asap... to discuss how we are going to achieve a solution".
He added that he was studying the FCO letter "with legal and political experts" to "fully understand where that leaves us".
He added: "That all said, clearly a positive step forward but we won't rest until we get justice for Harry."
On Friday, the Prime Minister said America was "absolutely ruthless" in its safeguarding of Ms Sacoolas following the decision to grant her diplomatic immunity.
Boris Johnson said although President Donald Trump was sympathetic towards Mr Dunn's family's views on the use of diplomatic immunity, the US is "very reluctant" to allow citizens to be tried abroad.