A chief constable has written to the US Embassy in London demanding the return of an American diplomat's wife who is a suspect in a fatal crash inquiry.
Harry Dunn, 19, died when his motorbike collided with a car near RAF Croughton in Northamptonshire on 27 August.
The diplomat's wife, named as Anne Sacoolas, left the UK despite telling police she did not plan to.
Nick Adderley, of Northamptonshire Police, has urged the embassy to waive her diplomatic immunity.
He said he had appealed to US authorities "in the strongest terms".
Mr Dunn's mother, Charlotte Charles, said leaving the country was "such a dishonourable thing to do" and urged Ms Sacoolas to "come back". His father, Tim Dunn, said they needed to get the truth.
Ms Charles added: "We are not out to get her put behind bars. If that's what the justice system ends up doing then we can't stop that but we're not out to do that, we're out to try and get some peace for ourselves."
The US Embassy previously said "security and privacy considerations" precluded it from naming the suspect.
On Saturday the US State Department said diplomatic immunity was "rarely waived" but Foreign Secretary Dominic Raab urged the US Embassy to reconsider.
Under the 1961 Vienna Convention, diplomats and their family members are immune from prosecution in their host country, so long as they are not nationals of that country. However, their immunity can be waived by the state that has sent them.
Mr Adderley was asked on Twitter whether Ms Sacoolas was lawfully entitled to claim diplomatic immunity.
He replied: "The short answer is yes," adding that both he and Northamptonshire Police and Crime Commissioner Stephen Mold had written to the US Embassy, urging that the waiver be applied "in order to allow the justice process to take place".
The US State Department said on Saturday that the incident involved "a vehicle driven by the spouse of a US diplomat assigned to the United Kingdom".
Police said the suspect had "engaged fully" following the crash near RAF Croughton, a US Air Force communications station, and said "she had no plans to leave the country in the near future".
The US State Department has said it is in "close consultation" with British officials and has offered its "deepest sympathies" to the family of Mr Dunn.
"Any questions regarding a waiver of immunity with regard to our diplomats and their family members overseas in a case like this receive intense attention at senior levels and are considered carefully given the global impact such decisions carry; immunity is rarely waived," it added.