On a summer's day in 2019, Harry Dunn was riding his motorcycle near an army base used by US troops in Northamptonshire, England, when he was hit and killed by an American '"spy" driving on the wrong side of the road.
His family described the 19-year-old as "bubbly and outgoing" with a passion for riding motorbikes. He'd ridden more than 80,000 kilometres before his death.
The driver, 45-year-old Anne Sacoolas, fled the United Kingdom on a private plane 19 days later, shielded by diplomatic immunity asserted on her behalf by the United States government as the "wife of a diplomat".
Harry's death started a three-year tug of war between the US and the UK, as his parents followed their pursuit of justice to the White House.
Sacoolas has never returned to the UK and appeared via video link at the Old Bailey on Thursday (local time) for her sentencing after the US government advised her not to travel to attend in person.
She was sentenced to eight months in prison, suspended for a year.
The protracted case has put a spotlight on diplomatic immunity and prompted calls for the rules to be changed.
The untouchable diplomat's wife
Sacoolas moved to the UK with her husband, Jonathan Sacoolas, and their children in July 2019.
She lived at RAF Croughton, a military base in central England, where her husband worked for the CIA.
Sacoolas also worked for a US security agency but was registered in the UK as the spouse of a diplomat "with no official role".
Under the Vienna Convention, spouses and dependents of foreign diplomats are entitled to full diplomatic immunity while in their host country.
Sacoolas had been in the UK for less than a month when, at about 8pm on August 27, she had a head-on collision with Harry's motorcycle while driving her Volvo SUV on the wrong side of the road.
Court documents show Harry sustained severe injuries but was able to tell police officers what had happened.
He died later that evening in hospital.
Sacoolas initially cooperated with police, agreeing to meet them the following day to answer questions about the fatal incident.
But the investigation stalled when the officers were told she was the wife of a diplomat.
Adjunct associate professor at the University of Sydney Law School Alison Pert said British police were powerless in the face of her diplomatic immunity.
"She could not have been arrested because she was inviolable, so she could not have been physically prevented from leaving the country and she could not have been prosecuted at that point," Dr Pert told the ABC.
The US government refused the UK's request to waive the diplomatic immunity, and instead it arranged for a private plane to return Sacoolas and her family to the US.
In a statement released by her lawyers, Sacoolas said she was "terribly, terribly sorry for the tragic mistake" and she extended "her deepest sympathy to Harry Dunn's family".
Back home in Virginia, Sacoolas no longer qualified for diplomatic immunity but was out of Britain's reach.
To New York and the White House
Harry's parents, Charlotte Charles and Tim Dunn, were not told the police could not charge their son's killer until after she had left the country.
The Dunn family launched a global campaign to have Sacoolas returned to the UK and held accountable for Harry's death.
Mark Stephens, an international lawyer with Howard Kennedy law firm who took on the Dunn family case as a pro-bono representative, said the US government underestimated the public backlash to the teenager's death.
"I think the Americans hoped to secrete their spy back to America and the incidence of her killing Harry Dunn would have been a small footnote in history," Mr Stephens told the ABC.
"Ordinary, decent people think her behaviour was reprehensible, beyond the pale, and that's why this has touched a nerve globally."
In October 2019, then-British prime minister Boris Johnson made a personal appeal to his US counterpart at the time, Donald Trump, asking for Sacoolas to be sent back to the UK to face charges.
The request was rebuffed at all levels.
Taking matters into their own hands, the Dunn family raised money to travel to New York to ask the American public for support.
"When the Dunn family went to America and explained on national TV their case and how this woman had essentially skipped away … the American public were horrified," Mr Stephens said.
While in New York, the Dunn family was invited to the White House to meet with Mr Trump.
Harry's parents agreed to meet, hoping to ask for Sacoolas to be extradited to the UK.
"He had Sacoolas in an outer office to the Oval Office … and tried to get them to essentially forgive Mrs Sacoolas right there and then," Mr Stephens said.
"Essentially Mrs Dunn said: 'No, not unless there's accountability.'"
As Mr Trump started to leave the office, he was interrupted by Harry Dunn's mother, Mr Stephens said.
"Mrs Dunn very politely said, 'Mr President, what would you have done if it was your child that was killed in this way?'"
"That struck a chord with Donald Trump. That hit home to him, and he stopped and he turned and he looked back at Mrs Dunn and he said: 'I'd probably do what you're doing Mrs Dunn.'"
The family did not meet with Sacoolas. Afterwards, Mr Trump told reporters Mr Johnson had asked him to see Harry's parents.
The UK's High Court heard then US national security adviser Robert O'Brien was also at the meeting and told the Dunn family that Sacoolas "was never coming back".
The transatlantic dispute over an 'utterly unacceptable' case
Four months after Harry's death, Northampton police charged Sacoolas in absentia with dangerous driving causing death and began extradition proceedings.
The US State Department condemned the extradition request as an "egregious abuse … that would establish a troubling precedent".
It was the first time the US had ever denied an extradition request from the UK.
In response, British MP Jeremy Hunt said the US government wasn't treating the UK as an ally.
"It is totally and utterly unacceptable that she is not facing justice in the UK," Mr Hunt told Sky News UK.
"If we're going to be an alliance, we need to treat each other like allies, and that is not happening."
Lawyer Mark Stephens believes it was Sacoolas's highly secretive role within the US government that prevented the White House from giving her up.
"She was working as a spy for the National Security Agency of America and perhaps that explains why the Americans were so keen to grant her diplomatic immunity," Mr Stephens said.
A change of leadership in the US in 2020 saw a change in tone.
US President Joe Biden said he was "actively engaged" in the case and in November this year Sacoolas pleaded guilty via video link to the lesser charge of careless driving.
Despite the Dunn family's wish for Sarcoolas to face court, she did not return to the UK for the sentencing hearing on Thursday.
The judge handed down an eight-month prison term, suspended for 12 months, meaning Sarcoolas would only face prison if she commits another crime in Britain in the next year.
"Anne Sacoolas has a criminal record for the rest of her life," Harry's mother said outside court.
"That was something she never thought she'd see, something the US government never thought they'd see.
"Harry, we done it. We're good, we're good."
Should diplomatic immunity be scrapped?
Under the current arrangements, a person's level of immunity is dependent on rank and "ranges from immunity from criminal and civil and administrative jurisdiction to immunity for official acts only", according to the Crown Prosecution Office.
Harry Dunn's death prompted a review of the immunity agreements in Britain.
As a result, the families of American staff working at RAF Croughton will no longer be protected by diplomatic immunity for "acts performed outside the course of their official duties".
Mr Stephens says the rules around diplomatic immunity more widely needed to be changed.
"The structure of diplomatic immunity relied on days when people were professional … people behaved with decency and appropriateness," Mr Stephens told the ABC.
"It's clear that that doesn't happen anymore."
Mr Stephens also said that in previous decades, the arrangement was "limited to very few people".
Currently about 23,000 individuals in the UK have diplomatic immunity, according to the BBC.
Diplomatic immunity was designed to protect diplomats and their families from hostile regimes but is now being used in cases of modern-day slavery, murder and family abandonment.
"I don't think the public at large around the world will tolerate immunity being given for acts of complete wrongdoing with no accountability," Mr Stephens said.
"… There's got to be a level of accountability where people commit crimes that otherwise they would stand charged for."
Dr Pert agrees the way diplomatic immunity is applied can be problematic, but says it would be difficult to change the rules.
"To fix this we would have to amend the Vienna Convention on Diplomatic Relations, which has been around for 60 years," she said.
"… We can't [change the rules] without having a full-blown conference of 194 countries meeting to amend it. Some might say, 'yes, it ought to be amended', but it would be very, very hard to do."
