Harry Dunn's family has told Sky News they will take legal action against the Foreign Office over the way the government handled the death of their son.
The teenager's parents, Charlotte Charles and Tim Dunn, have instructed a top-level legal team to seek a judicial review into the way his case was dealt with.
Human rights barrister Geoffrey Robertson, who has defended boxer Mike Tyson and former Brazilian president Lula da Silva, will be on the team.
Mrs Charles and Mr Dunn have also condemned Northamptonshire Police's decision to send officers to the United States to interview Anne Sacoolas.
She is accused of crashing into Harry, 19, on his motorbike outside a US spy base as she drove on the wrong side of the road on 27 August, but then left the UK after being granted diplomatic immunity because of her husband's job.
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The family are referring the case for review by the Independent Office for Police Conduct.
British police confirmed on Tuesday they will interview Mrs Sacoolas under caution in the US after she requested to be interviewed by Northamptonshire Police in her home country.
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Being interviewed under caution means Mrs Sacoolas will have the right not to answer questions if she does not want to – but anything she does say can be used in a legal case.
Chief Constable Nick Adderley said Mrs Sacoolas not being in the country "frustrates the investigation, but does not stop it", and that police had now passed the case on to the Crown Prosecution Service.
He added: "The suspect cooperated with police at the scene and spoke with authorities there. Officers attended the home address of the suspect next day (28 August), and again she fully cooperated."
Mrs Sacoolas, 43, has offered an apology over the fatal crash outside RAF Croughton, but has been told by Harry's mother that "sorry doesn't cut it".
