The Fiat involved in the death of Princess Diana remains unsolved to this day, according to French investigators.
Today, August 31, marks 25 years since the fatal car crash in which Diana, her driver Henri Paul and her partner Dodi Fayed lost their lives.
Despite being a quarter of a century since the tragedy, theorists continue to speculate whether the accident was orchestrated.
A number of these questions were raised in the recent Channel 4 docu-series Investigating Diana: Death in Paris, which examines the two investigations into the incident by French and British police.
Ultimately, Diana's death was ruled an accident as a result of Paul trying to flee paparazzi, only to lose control of the Mercedes while inside the Pont de l'Alma tunnel in Paris.
But many have suggested that the car was tampered with, while others have turned their attention to the disappearance of the white Fiat Uno that was believed to have collided with Diana's car on the morning she died.
A couple claimed to have witnessed the Fiat emerging from the tunnel with a male driver who was said to be focused on his mirrors, and the investigation reported traces of white paint on the black Mercedes.
While French detectives don't believe the driver was responsible for the crash, they voiced their frustration at never locating what could've been a major clue as to uncovering more evidence.
Fabrice Cuvillier of the Brigade Criminelle said on the documentary: "It’s not a hallucination. It’s not something we threw out to create a diversion. It exists. We did not find this Fiat.
"But it would be dishonest of me to look you in the eye and say ‘we didn’t let the Fiat Uno slip through’. I don’t think so, but I’m not 100 percent sure."
Cuvillier's colleague Eric Gigou added: "We did everything we could to understand what happened and more than 1,000 people were interviewed in the investigation by the French authorities.
"In my mind, the only door that remains open is the testimony of the driver of the Fiat Uno."
Martine Monteil, head of the Brigade Criminelle, also spoke about the missing puzzle piece, stating: "The whole of the world has struggled to accept that the Princess of Wales died in a mundane accident."
She continued: "I have frustration about the Fiat Uno because I like a well-finished business. For sure, it's out there. Unfortunately we don't have it.
"But you know the driver of the Fiat Uno, he's not the real culprit. He's driving along quietly and then a Mercedes arrives at high speed and bumps into him. The responsibility remains with the Mercedes."
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