Harry Dunn's family are suing the Trump administration for "lawless misconduct" and starting legal action against Anne Sacoolas – the driver involved in the crash that killed the teenager.
The 19-year-old died after being knocked off his motorbike near RAF Croughton, a US spy base, on 27 August.
Mrs Sacoolas is believed to have been driving on the wrong side of the road and returned to America soon after the incident.
She was granted immunity from prosecution because her husband is a US diplomat.
Harry's family have been fighting a high-profile campaign to get Mrs Sacoolas to return to the UK to answer questions.
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They met President Donald Trump at the White House earlier this month – Mrs Sacoolas was in the building but they turned down an unexpected last-minute offer to meet her.
The family have already started a case against the UK Foreign Office over the decision to grant her immunity.
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Spokesman for the Dunns, Radd Seiger, said their legal fight is now moving to the next level and will be a "memorial" to Harry.
"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," said a statement.
"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 Seiger said the US government had tried to "twist and contort the laws on diplomatic immunity" and called the White House attempt to get the family and Mrs Sacoolas in the same room a "disgusting stunt".
Shortly after their meeting with Mr Trump, Harry's parents praised the president's apparent sincerity but their anger was clear in today's statement.
"The Trump administration is not only hell bent on breaking international laws, rules and conventions on diplomatic immunity, but they have no care or concern for the welfare of Harry's family or any real intent on finding a solution," said theiRead More – Source
