Harry Dunn's family suspects Anne Sacoolas may have been distracted by her phone at the time of the fatal crash in Northamptonshire in 2019, lawyers have claimed.
According to court papers, the American driver's phone records for the day of the crash near Croughton in August two years ago appear to have been deleted, which she denies.
Sacoolas has been 'evasive, non-responsive and inconsistent' on the issue, according to court papers seen by this newspaper today (Monday, August 9).
The United States government has blocked information on her and her husband's intelligence work over national security concerns.
The victim's family's spokesman, Radd Seiger, said: "As our lawyers have made clear consistently, we have no wish to lay bare their national security secrets.
"We just want to get to the bottom of things and that is just what we intend to do."
Harry, 19, from Charlton, was killed after his motorcycle was involved in a crash with Sacoolas' car, which was on the wrong side of the road, on the B4031 on August 27, 2019.
The driver controversially claimed diplomatic immunity as her husband, Jonathan, was working for the US government at RAF Croughton and left the country.
She has been charged with causing death by dangerous driving but the US State Department has repeatedly refused to extradite her.
Harry's family are suing Sacoolas and her husband for damages in the Alexandria District Court in the US state of Virginia, which previously heard the pair's work in intelligence was a factor in them leaving Britain.
As part of the civil claim, the teenager's parents, Charlotte Charles and Tim Dunn, have asked Sacoolas for her phone records and work at the time of the crash.
Mr Seiger added: "When you lose a loved one following a traumatic event, as Harry’s parents have, preserving what little is left of one’s mental health becomes paramount.
"As painful as it is, it is well established that knowing and understanding all of the facts as to what happened is an essential part of that process
"Charlotte and Tim are entitled to see that the facts are established in the first place and this usually happens during the course of civil and criminal proceedings following serious road traffic collisions.
"The US government and Mrs Sacoolas can blame no one other than themselves for the scrutiny that they are now coming under. This is what justice systems are designed to do."
Last month the US government filed a motion to suppress the Sacoolases employment details because of the impact on national security.
Harry's parents' lawyers have now submitted documents in opposition, which say they are not interested in the details of their work.
The papers also refer to Sacoolas' phone records, which they also requested to find out if she was distracted at the time of the crash, and the response 'raises more questions than it answers', they say.
She initially said she got a new SIM card when she returned to the US and there was no data available for August 2019, plus Mr Sacoolas binned his old phone and got a new one, the court papers state. Nonetheless, they had the old SIM card examined to retrieve any call or text data, which found one text but no calls for August 27 - the content of the text has not been revealed.
However, Sacoolas has previously said she called her husband shortly after the crash and calls were found on the days before and after by the examiner.
This 'raises the possibility that [she] was distracted by her mobile telephone and establishes that relevant phone data was deleted', Harry's parents' lawyer's court paper states.
Mr Seiger said: "Charlotte and Tim are on a search for the truth, and will not be deflected from that. The US government continue to do everything within their power to stop them."
Sacoolas' lawyers have been contacted for comment.