The suspect in teenager Harry Dunn's death has asked to be interviewed under caution as officers urge the family's spokesman to exercise restraint.
Anne Sacoolas left the UK while claiming diplomatic immunity after being involved in a car crash that killed the 19-year-old outside a US military base in Northampton in August.
Mrs Sacoolas is the wife of US diplomat Jonathan Sacoolas.
Speaking during a press conference, Nick Adderley, Chief Constable of Northamptonshire Police, said the suspect had asked to be interviewed by UK police officers in the United States under caution.
He said that she had asked to be interviewed by officers from Northamptonshire Police so that they could see the "devastation" the incident had caused her.
Mr Adderley said: “Lawyers have clearly stated that the suspect wants to be personally interviewed by officers from Northamptonshire Police in order for them to see her and the devastation this has caused her and her family.
“She did not want to provide a pre-prepared statement which is her right to do so. We do understand from colleagues in the US that the family is utterly devastated.”
"She did not want to provide a brief prepared statement, as is her right."
The Chief Constable told the press that officers were currently waiting for visas to the US.
"As soon as they have visas they will travel to the US", he said.
"They are not currently in the country."
Mr Adderley said that police would not be naming the suspect until the file of evidence was complete.
“A file of evidence has been handed to the Crown Prosecution Service but as you will appreciate that file is incomplete, you can’t complete the file until you have an account from the suspect and that is one of the reasons why we are not naming her", he said
He added: “From the police’s point of view we have to make sure we maintain the integrity of all of the evidence and that it is not skewed by (the diplomatic immunity debate) to ensure a fair trial should we get to an extradition position and she comes back to the UK.
“We don’t want to jeopardise that by not affording her a fair trial.”
Mr Adderley admitted that the suspect being in the US had frustrated the investigation, but denied that it had stalled it.
“This investigation has not stalled, it has not slowed down", he said.
“The suspect not being in the county clearly frustrates the investigation but it does not stop it.”
Mr Adderley refused to reveal how the Dunn family had learned the suspect had left the UK, but said it had not been a leak from Northamptonshire Police or the Foreign and Commonwealth Office.
“It was unfortunate but it was legitimate”, he said.
When asked if Mrs Sacoolas would have been charged by now had she been British he said it was unlikely as on average it takes 16 weeks for a fatal collision file to be put together.
“It is likely that she would have been interviewed by now and the full file may be being talked through with the Crown Prosecution Service but we would not be any further forward,” he said.
Mr Adderley also called on Radd Seiger, spokesman for Harry Dunn’s family, to “exercise constraint”.
He said: “I urge the family spokesman to exercise constraint in his commentary as the case moves forward.
“I understand the emotion and I understand the anxiety,
“I also understand the will and the want for answers to questions the family are asking.”
Harry Dunn's family travelled to the US to meet President Donald Trump.
While Harry's parents Tim Dunn and Charlotte Charles were in the White House President Trump offered them the opportunity to meet Mrs Sacoolas, who was waiting in the room next door.
The family declined the offer.