Whatever happened to the diamond that went missing in F1 crash?

Where were you between the hours of 1pm and 3pm on 23 May 2004?

If you were in Monaco, consider yourself a suspect - or at least a witness - in Formula 1's biggest unsolved mystery.

A $300,000 diamond was last seen stuck to the front of an F1 car before it crashed on the first lap of the Grand Prix and it still has not been found 22 years later.

Did someone pick it up? Was it swept up with all the debris? Did it slip down a drain? Was it even a real diamond?

Someone, somewhere, knows something.

The reason why a 1.4 carat diamond was attached to the most delicate part of a car that reaches 200mph in a race was straightforward: publicity.

Jaguar Racing's results on the track had been mediocre at best since becoming an F1 team in 2000 and by 2004 its parent company Ford had decided it would be pulling them out of the sport.

"My job flipped from primarily running the team to primarily selling the team and finding a new owner or they would shut it down," former team principal Tony Purnell tells BBC Sport.

"It was probably the worst year of my life. Particularly because for the first few months I was sworn to secrecy."

His team needed some good PR to divert attention away from performance and improve its appeal.

They had enjoyed a successful promotional weekend in Silverstone the previous season thanks to a tie-up with Terminator 3 and so director of communications Nav Sidhu was looking to recreate the magic with another bit of help from a movie.

"I'd heard on the grapevine, around about the winter of 2003, that they were making Ocean's Twelve and we discovered that they were shooting some of the scenes in Monte Carlo," Sidhu says.

"One thing led to another and before you knew it, we had agreed [a deal] with George Clooney, Brad Pitt and Matt Damon."

Sidhu had arranged with legendary Hollywood producer Jerry Weintraub to have the film's branding and stars take over the team for the Monaco weekend.

The film plot centred on an audacious theft of a diamond-encrusted Faberge egg. Sidhu decided he wanted some sparkle on his cars too at the most glamorous race in the F1 calendar.

Sidhu negotiated with diamond company Steinmetz that the two Jaguar cars would have gems - which would today be worth about $1m in total - attached to them.

What happened next, though, was not part of the script.

While the champagne corks were popping on nearby mega yachts in the principality, the diamonds were being hand-delivered into the garages. There were two that would be mounted on to the car and a larger gem just for the photos.

The diamonds for the cars were encased by steel and fixed to the nose cones. One on experienced driver Mark Webber's car and one on rookie Christian Klien's.

Webber was starting from 11th place in the grid and Klien - in only his sixth race - was starting from 14th. They weren't expected to challenge for the podium, but they were expected to bring the diamonds back.

Monaco's street circuit is demanding, with narrow roads, tight turns and a tunnel.

Overtaking is difficult and crashes are common - as Klien soon found out.

In a chaotic first lap, the Austrian made contact with one of the Jordan cars exiting the Mirabeau corner. This damaged the front of his car - where the diamond was - and led to a slow collision with the barriers at the famous Loews hairpin.

Klien climbed out unhurt but the front of the car was crumpled.

It was not long before Sidhu had the diamond company on the phone asking if they would get their diamond back.

"I can't remember what I answered, but it certainly wasn't 'yes'," he says.

He couldn't even get on to the track to have a look as the race had another 76 laps to go and only then would the car - which had been lifted off the track by a crane and left behind the barriers - return to the garage.

"I was consumed with getting to that spot as quickly as I possibly could," Sidhu says.

"That hour and a half waiting for the race to finish felt like a day and a half, every single lap was just like pulling teeth."

By the time he had the chance to have a look, there was no sign of the diamond.

But there were plenty of theories.

Theory: it was not a real diamond

Sidhu completely denies the rumours of a fake diamond.

"I've learned that any diamond company is not going to go out there, particularly in the public domain, and use fake diamonds because clearly there's a high risk of being caught," he says.

"Had we used a fake diamond in that car and what took place took place, then clearly the embarrassment and the disrepute it would bring Jaguar, and Formula 1 for that matter, was too high risk.