The distraught mother of a teenager killed in a road crash has appealed directly to the wife of a US diplomat who subsequently claimed diplomatic immunity pleading for her to return to the UK.
The grieving parents have also warned that they won't let the matter rest until justice is served.
Harry Dunn was struck close to RAF Croughton, an American spy base in Northamptonshire, back in August.
The tragic 19-year-old was riding his motorbike when an unnamed woman "pulled out of the base onto the wrong side of the road" and hit him head-on.
He was rushed to hospital and died from his injuries soon after but the suspect has not returned to the country, instead claiming diplomatic immunity after going home to the States.
Diplomatic immunity means envoys cannot be sued or prosecuted in their host countries.
American officials have warned the suffering parents that "immunity is rarely waived" but they say they cannot move forward until she returns.
Speaking to the PM Programme on BBC Radio 4, Charlotte Charles said: "We're really hoping to try to get her back, from me as a mum, to her as a mum.
"You just hope that he [Foreign Secretary Dominic Raab ] can try to get through to her, that we don't wish her any ill harm - but we don't understand how she can just get on a plane and leave our family just utterly devastated.
"If we don't get any luck over here, then we will go over there."
The victim's father Tim Dunn told Sky News: "We're disgusted, appalled - how she could be having this cloak wrapped around her?
"I'm angry that someone could do this and then get on a plane and go. I can't believe she's living with herself.
"We can't quite understand this is actually happening, or has been allowed to happen."
Family spokesman Radd Seiger said it is understood British authorities asked their US counterparts for immunity to be waived "several times".
He said: "They've been told the answer is no, we've learnt via the police. The answer has come back as no."
In a statement, the US Embassy in London said: "We express our deepest sympathies and offer condolences to the family of the deceased in the tragic August 27 traffic accident involving a vehicle driven by the spouse of a US diplomat assigned to the United Kingdom.
"Embassy officials are in close contact with the appropriate British officials on this matter.
"Due to security and privacy considerations, we cannot confirm the identity of the individuals involved, but we can confirm the family has left the UK."
