Northamptonshire Police have conducted an interview with the suspect in the investigation into the death of 19-year-old Harry Dunn.
It is understood the force have passed the details of the interview to the Crown Prosecution Service.
Anne Sacoolas is believed to have been driving on the wrong side of the road when she hit 19-year-old Dunn’s motorbike outside RAF Croughton on August 27.
The 42-year-old, a wife of a US diplomat, was granted diplomatic immunity after the case, which has since been disputed by the lawyers acting on behalf of the teenager’s family.
Chief Constable Nick Adderley had faced calls from the family for his resignation after he commented on potential legal action by them against Mrs Sacoolas by saying: “How sad but how predictable.”
Adderley has since deleted the tweet.
Northamptonshire Fire, Police and Crime Commissioner (PCC) Stephen Mold has said he has spoken to Adderley about keeping force communication “professional and sensitive at all times”.
The police chief has since said he “meant no offence” and apologised if his tweet had been “misconstrued or misinterpreted”.
The family’s lawyers have since instructed the family that they should now take legal action against Northamptonshire Police for their conduct throughout the investigation.
Radd Seiger, the spokesman for Dunn’s family, said: “They are now going to be subject to legal action.
“The courts will review their decision making processes as well as that of the Foreign and Commonwealth Office.
“The letter has been drafted and the lawyers have said it is good to go.
“The courts should be reviewing their various decisions with how they proceeded with the investigation and how they have supported the family”.
In a statement about Adderley’s tweet, Seiger, said: “We call on (Chief Constable Nick Adderley) to resign immediately following his disgraceful now deleted tweet on Tuesday.
“Mr Adderley has displayed a staggering degree of unprofessionalism with this tweet such that he no longer commands the confidence of the family.
“This is simply the straw that broke the camel’s back, coming as it does on the back of apparent misconduct and/or incompetence in the handling of this investigation and their egregious breaches of the victims code in not supporting the family or keeping them informed.
“It is with a heavy heart that Harry Dunn’s family feel that Mr Adderley should now do the honourable thing and resign.”