A completed file of evidence on the death 19-year-old Harry Dunn has been handed over to the Crown Prosecution Service.
Northamptonshire Police confirmed that it had completed the file after conducting an interview with the 42-year-old suspect in the case, Anne Sacoolas, in the US.
Mrs Sacoolas is believed to have been involved in a collision with the teenager's motorbike outside RAF Croughton in Northamptonshire on August 27.
She claimed diplomatic immunity after the incident and returned to the US, sparking an international controversy.
Reacting to the file being handed over, the family's spokesman Radd Seiger said: "We are pleased that at long last Northamptonshire Police have been able to complete their investigation and hand the file over to the CPS.
"On September 26 the family were told they had less than 1% chance of somebody being held accountable for the loss of their son.
"I believe we would not be in this scenario were it not for the incredible determination of the most courageous and dignified family I have ever met - who have moved heaven and earth to get justice for their son on both sides of the Atlantic."
It comes after US President Donald Trump said Mrs Sacoolas had a “compelling story to tell” when he met her at the White House.
Describing his efforts to broker a meeting between Mr Dunn's parents and Mrs Sacoolas, Mr Trump said in an LBC radio interview with Brexit Party leader Nigel Farage: "I had a meeting set up but all of a sudden I guess lawyers got involved.
"I had a meeting set up, they were both in the White House. I met with the parents of the young boy, very nice people."
The US president added: "I met with the young lady that was driving the car and she brought a very compelling story to tell.
"And then they were in separate rooms and what I wanted was to introduce them to each other so they could really grieve together - the parents didn't want to meet her."
Asked if there were circumstances where Mrs Sacoolas could come back to the UK to face charges, Mr Trump said: "Well, I would have to see what the final facts are.
"And, I'll take a look at the final facts. She's represented by a lawyer.
"As you know, the parents are represented by a lawyer and from the time I talked to Boris to the time I met with them, but they were both right next to each other in the White House.
"I was in the Oval Office with the parents and the young lady was in a room right next to the Oval Office, but the parents decided, in their wisdom, and it is certainly their choice, not to see her. I can understand that too."
