Tim Dunn says the past week has been "a whirlwind" for him and his family after they have been quizzed in interview after interview by national media.
"It's so hard to believe that our Harry is in the middle of something as big as this," Tim told the Chron. "We would never have dreamed it. It's crazy."
Harry Dunn, of Charlton, near Brackley, died in hospital earlier this year after his motorcycle collided with an oncoming car on the B4031 Park End, Croughton, on August 27. He was 19.
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But a scandal erupted this week after it was revealed a suspect in the case Anne Sacoolas - the wife of an American diplomat who was staying at RAF Croughton at the time - left the UK and flew back to the US after claiming diplomatic immunity.
In the past few days, Tim and Harry's mum Charlotte have been asked to directly appeal to Mrs Sacoolas and plead with her to return to the UK.
But for Tim, he only wants to ask her what happened to his son.
"I just really want to know the whole truth of the accident," said Tim. "We know the ambulance took 50 minutes to get there. I just want to know if she went to comfort my son. It pains me to think my son was there for 50 minutes - his arms broken, legs broken, pelvis broken - lying in a ditch. Just waiting."
Harry's death and Mrs Sacoolas' claim to diplomatic immunity have been met with anger across the UK. Thousands of people are now calling on the US to revoke the claim and return her to the UK.
Tim said: "We believe she is not entitled to the immunity. Diplomatic immunity is there to protect diplomats if they are in danger.
"She was never in danger - she was driving on the wrong side of the road.
"For the first few days after the accident, we were confident that it would almost be straightforward. The police told us she said she wouldn't leave the country, that she admitted it was her fault, and the CCTV showed she was on the wrong side of the road.
"We thought it would be quite quick to prove it."
In a statement on October 5, Northamptonshire Police said the suspect had "engaged fully" with the force after the accident, and had claimed she had "no plans" to leave the country.
But instead, Mrs Sacoolas was able to fly back to the US by claiming diplomatic immunity.
It comes as Tim and his family are today (October 9) meeting with the secretary of state for foreign affairs Dominic Raab.
Tim said: "Hopefully Dominic will be able to put us in the picture as to what's going on.
"We are as much in the dark as everyone else. We know as much as what's in the papers.
"You wouldn't believe how much of this has felt like smoke and mirrors. The US Secretary of State and the US Embassy have been silent. We've not had heard a word. No letter, no phone call - not a word from Croughton base.
"We're just trying to get the truth for Harry."
Thousands of people across the UK have taken to social media in past week with the hashtag #JusticeForHarry to call for Mrs Sacoolas to return to Britain.
Meanwhile, both Dominic Raab and PM Boris Johnson have asked the US to "rethink" the granting of diplomatic immunity.
In a statement, the US State Department said diplomatic immunity was "rarely" revoked.
Tim said: "I'd like to think the UK government is doing their best. This is quite alien to us so we don't know if this is moving slowly or quickly.
"They've asked for a waiver twice and Boris Johnson spoke about it on Monday.
"I want to think they're doing the best for us.
"For us as a family, it's like we're on auto-pilot. It's been a lot of trips to London. I think his grandparents are struggling the most with it all.
"You wouldn't believe the amount of friends Harry had. He was so popular."