The mother of Harry Dunn has urged presidential candidate Joe Biden to reconsider the US's position on her son's alleged killer should he win the election.
In a video message to Mr Biden, Charlotte Charles said her "heart goes out" to him after the loss of his son in 2015 – but said her family needed justice in order to "help us on the path" to recovery.
Mrs Charles's 19-year-old son was killed when his motorbike crashed into a car outside a US military base in Northamptonshire on August 27 last year.
The US asserted diplomatic immunity for suspect Anne Sacoolas following the crash and she was able to return to her home country – despite later admitting she had been driving on the wrong side of the road for 20 seconds before the teenager's death.
US Secretary of State Mike Pompeo rejected an extradition request for 43-year-old Sacoolas after the CPS charged her with causing Mr Dunn's death by dangerous driving – describing the decision as "final".
Mrs Charles appealed to Mr Biden to "do your best to amend" the situation – saying Sacoolas "walking free" was "tearing us apart as a family".
In her video message, seen by the PA news agency, Mrs Charles said: "I would imagine you are aware of Harry's case and our campaign – we've been running it for a year now.
"Very, very sadly, a year on, Anne Sacoolas has still not been sent back here to the UK to face our justice system.
"I please urge you, should you win on November 3 to please reconsider the position the US has taken against us – and when I say us I don't just mean myself and the rest of the parents, I mean us as the UK as well.
"We never, ever expected to be in this position. We never thought the lady who is responsible for taking our son's life would have been able to fly home to the US and evade as best she could the UK justice system."
Describing her family's emotions to Mr Biden, Mrs Charles continued: "It's tearing us apart as a family. We are not only trying to live without Harry every day – the pain now is far worse than it was this time last year because we are no longer numb and no longer in shock.
"So we have to live every day, knowing that Anne Sacoolas is still walking free, tucking her three children into bed at night, doing her everyday jobs and tasks – whilst we're still sat here suffering.
"All we have ever asked of the US and her, is to just allow her to face the UK justice system. It's totally and utterly morally wrong."
Mrs Charles continued: "Justice is so important to us – it doesn't matter what that justice looks like.
"All we ask is for her to face the UK justice system – that's not too much for anyone to ask.
"I know you've lost a son yourself, albeit in different circumstances, but my heart goes out to you because of that.
"Any parent who loses a child never fully recovers – but getting justice can certainly help us on the path to doing so."
Urging Mr Biden to take an interest in the case should he win the election on November 3, Mrs Charles said: "We have many people in the UK who are extremely angry. We've always thought of the US as an ally and that seems to have completely fallen apart since they allowed Anne Sacoolas to return back to the US and walk away from what she's done.
"Although we've had the anomaly amended, and no other family can go through what we've gone through, it still angers many, many people that there are so many US citizens working on UK soil.
"One US citizen has taken the life of my boy and is still not facing the justice system here in the UK for that. Please do your best to amend it."