Harry Dunn’s family is to sue crash suspect Anne Sacoolas, their spokesman in the United States has said.
The 19-year-old was killed outside RAF Croughton in a crash with a car owned by Mrs Sacoolas – a US citizen who left the UK claiming diplomatic immunity.
Family spokesman Radd Seiger said lawyers would also look at “lawless misconduct” of the US administration.
The Dunn family has already launched legal action against the Foreign and Commonwealth Office.
They have also referred Northamptonshire Police to the Independent Office for Police Conduct.
Mr Dunn died in hospital after his motorbike was involved in a crash near the RAF base in Northamptonshire on 27 August.
Mrs Sacoolas’ husband Jonathan is a US intelligence official who was working at the base.
Both the British and US governments agree that by returning to the US Mrs Sacoolas forfeited the right to diplomatic immunity.
Mr Seiger said it was clear “various agencies involved not only did not do what they were supposed to do, but have in fact become part of the problem”.
He said: “We are announcing today that we are bringing claims against both Mrs Sacoolas in the USA for civil damages as well as the Trump administration for their lawless misconduct and attempt to cover that up.
“No-one is above the law and the family are determined to ensure that this never happens to another family again.
“It will be Harry’s memorial. His legacy.”
Mr Dunn’s step-sister Larna Harber, who has travelled to the US to keep the case in the public eye, said the family had questions which needed answering before they could grieve.
She said: “We just want her to come back and answer our questions because we don’t actually know any more of what happened that night.
“He was laid on the verge waiting for an ambulance for 50 minutes but who was with him?”
Last week Northamptonshire Police Chief Constable Nick Adderley said Mrs Sacoolas would be interviewed under caution in the US.
The BBC has attempted to contact Mrs Sacoolas’ lawyer for comment.