A diplomat's wife, who had been helping police following the death of a Croughton teenager in a road accident, has returned to the United States.
Harry Dunn, 19, died in hospital earlier this year, following the collision in Park End, Croughton. He was riding a motorcycle at the time of the head-on collision with a car.
In a statement issued on Friday night, Detective Superintendent Sarah Johnson, confirmed that a 42-year-old American woman was being treated as a suspect in the investigation and that she had now left the country.
“Northamptonshire Police followed all of its usual procedures following the incident, including liaising closely with the suspect, who engaged fully with us at the time and had previously confirmed to us that she had no plans to leave the country in the near future," Det Supt Johnson said.
“Due process was also followed in seeking the necessary documentation to allow for the arrest and formal interview of the suspect, and the Force is now exploring all opportunities through diplomatic channels to ensure that the investigation continues to progress.
“We are also working closely with the Foreign and Commonwealth Office in an effort to come to a resolution regarding this matter," she added.
His family paid tribute to him, describing him as a "caring and loving young man".
On a BBC news programme his mother Charlotte said the family had been left 'utterly devastated'. The Standard tweeted her heartfelt message 'We have nothing. No justice. We have nothing to put our minds at rest that she's even remorseful'.
South Northants MP Andrea Leadsom tweeted: "I met Harry’s family yesterday. They are totally heartbroken. We have to get proper justice for Harry and closure for his family."
It is understood the suspect is the wife of a US diplomat and therefore has immunity which is 'rarely waived'. The BBC said foreign secretary Dominic Raab had asked the US embassy to reconsider and shadow foreign secretary, Angela Rayner tweeted her plea for fairness. "If we stand for anything it’s the common rules of fairness. Harry & his family have been wronged. You have to act. The diplomatic rules should not be used in this case," she said.
Mrs Charles told the BBC: ""If we don't get any luck over here, then we will go over there."
Det Supt Johnson said: "Harry Dunn’s family deserve justice and in order to achieve this, a full and thorough investigation, with the assistance of all parties involved, needs to take place.
“Northamptonshire Police is committed to ensuring justice for Harry and specially trained officers continue to support the Dunn family in their loss, including keeping them fully informed of all developments in the investigation.”