The family of Harry Dunn are bringing a private criminal prosecution against Dominic Raab, claiming that the foreign secretary broke the law in his dealings with the case.
Mr Dunn was killed while riding his motorcycle last August in a head-on collision with American Anne Sacoolas.
The diplomat's wife had pulled out on to the wrong side of the road after leaving a US intelligence base at RAF Croughton in Northamptonshire.
She claimed diplomatic immunity and returned to America, and was later charged with causing the 19-year-old's death by dangerous driving.
Harry's family claim that the Foreign Office allowed Mrs Sacoolas to go.
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"We need this for everybody to know how the decisions were made and why the procedures and guidelines weren't followed and for me to get some justice and a bit of peace," Harry's father Tim Dunn told Sky News.
On 14 September, a foreign official texted a US official to say: "I think that now the decision has been taken not to waive (immunity) there's not much mileage in us asking you to keep the family here.
More from Anne Sacoolas
"It's obviously not us approving of their departure but I think you should feel able to put them on the next flight out."
Harry's family claim that Mrs Sacoolas left the next day.
Their spokesman and adviser Radd Seiger told Sky News: "There's a very clear rule that it's for the police to establish who has immunity.
"That rule was broken and we allege it constitutes a serious instance of misconduct in a public office.
"That effectively stopped their investigation and we say that amounts to perverting the course of justice – two potentially serious crimes."
A private prosecution is a prosecution started by a private individual who is not acting on behalf of the police or other prosecuting authority.
There are a number of organisations that regularly prosecute cases before the courts of England and Wales but they do so as private individuals, using the right of any individual to bring a private prosecution.
Legal commentator Joshua Rozenberg said it was unusual to bring a prosecution against a government minister.
He said: "The courts have said it's a high threshold. Even to get a summons issued. Even harder to prove it.
"There is no doubt Mr Raab will defend it and say this is an abuse of the court process and not something the court should be involved in."
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