Parents Tim Dunn and Charlotte Charles are filing the suit in Virginia, where Sacoolas lives, in hopes of compelling her to return to England, turn herself in and face charges. The family's lawyer plans to rely on ancient English common law dating back to 1774, which says even though the offense may have been committed in one country, the accused can face charge in another. Harry's parents said this is about justice and closure.
"We're sort of in limbo. We're trying to our hardest to get this result for Harry and get the truth out there," Dunn told CBS News correspondent Imtiaz Tyab in an exclusive interview.
Almost four months after Harry was killed while riding his motorcycle, Dunn and Charles are set to meet with their new legal team in Washington.
"It is exhausting. It's 24/7, but as a family we feel this is the right way. We feel it's the way we have to go," Dunn said.
Sacoolas had just left the Royal Air Force Base Croughton in Northamptonshire, where her husband was stationed, when she hit Dunn while driving on the wrong side of the road. Sacoolas' legal team previously told CBS News she had no time to react before the crash and that she cooperated with local investigators.
"She needs to still face what she's done to us and take some punishment for that," Charles said, choking up with emotion.
The family has yet to meet Sacoolas face to face. But they came close back in October when they met President Trump at the White House. Sacoolas was waiting to meet them in a room nearby.
"It was quite bizarre really, looking back on it now," Charles said. "Thankfully, as a family, we discussed many scenarios, including the most bizarre and ludicrous one that we could come up with, which was the fact that Anne Sacoolas may well have been there."
"I think what Charlotte said, 'cause we talked about it, we already had like, in our minds, that if Anne was there, we were going to say no. Because as Charlotte said, it would have been unfair on her and on us," Dunn added.
Now, months after the crash, Harry's family said they're facing a new challenge: the holidays without their son.
"We're not doing Christmas this year," Charles said. "We use to have to chop the top off of the tree to get it into our house. There's not been a year gone by where both of the boys, Harry especially, is like, you know, 'When are we getting the tree? Make sure it's bigger and better this year, Mum."'
"It is going to be horrific this year. And I think the trouble is, it's going to be difficult from now on, every Christmas … because it was his favorite time of year," Dunn said.
We reached out to Sacoolas' lawyer about this new legal step, but did not receive any comment. Legal experts we spoke with said there are questions about jurisdiction if and when a lawsuit is filed here, including how much diplomatic immunity would extend to Sacoolas and how much it would apply now that she's back in the U.S.