By Tom Geoghegan
BBC News Magazine
Mark Felt's admission that he was Watergate's Deep Throat has solved one of the world's great mysteries, hitherto known only to a handful of people. But there are plenty of other secrets out there.
Even in a world which prides itself on its great knowledge and sophisticated detection methods, there are some questions only a few can answer.
Unsolved crimes, trade secrets and instances of political intrigue endure despite intense scrutiny from the media and the authorities.
Here are 10 things we still don't know.
WHAT HAPPENED TO JIMMY HOFFA?
The former leader of the Teamsters truckers' union disappeared from a Detroit restaurant in 1975 and his body has never been found.
Last seen in a restaurant car park
Investigators believe the 62-year-old Jimmy Hoffa may have been the victim of an underworld feud and he is thought to have fallen out with several organised crime figures.
He made the Teamsters one of the most powerful unions in the United States under his 10-year leadership which ended in 1967, when he was imprisoned for jury tampering and fraud.
Twenty-six years later in March 2001, a DNA match was made between Hoffa and hair found in the back of a car police suspected, but could not prove, was involved in his disappearance.
Last year, a biography of Teamsters official Frank Sheeran, who died in 2003, says Sheeran claimed responsibility.
The book's title, I Heard You Paint Houses, refers to the first words Hoffa apparently ever spoke to Sheeran. The phrase is a euphemism for murder because it implies your blood will splatter on the walls.
WHAT DID BLAIR TELL BROWN AT GRANITA?
The scene for one of the most talked-about episodes in British politics was Granita restaurant in Islington, north London.
Although most political commentators think they know what happened, no-one knows what was said. Except two men.
On 31 May 1994, Gordon Brown and Tony Blair met for dinner. The story goes that Brown agreed not to contest the imminent leadership contest. In return, Blair reportedly promised Brown a free hand in running the economy, and to step down after seven years.
There are no witnesses, but dozens of books and a television drama have speculated on "the deal".
WHERE IS LORD LUCAN?
The 7th Earl of Lucan vanished in November 1974, a day after the murdered body of his children's nanny, Sandra Rivett, was found at his London home.
Over the years numerous people have claimed sightings of the aristocrat, whose body has never been found.
The investigation reopened last year, with detectives examining existing police evidence and using new DNA techniques to try to solve the case.
WHAT'S THE RECIPE FOR COCA-COLA?
The secret to one of the world's most famous brands lies deep in a bank vault somewhere in Georgia, US. Its exact location is reportedly known only to between two and four Coca-Cola executives.
No sign of the recipe on the can
It is rumoured that measures are employed to protect the chosen few - the executives never travel together, and must approve a successor should one of them die.
Outlets which make the drink are simply supplied with syrups and other ingredients from Coca-Cola - but not the original recipe.
People have revealed what they claim to be the official recipe after analysing the drink, but Coca-Cola remains tight-lipped.
DID LEE HARVEY OSWALD ACT ALONE?
President John F Kennedy was shot dead in his car in Dallas, Texas, on 22 November 1963.
He was assassinated by Lee Harvey Oswald whose fingerprints were all over the area where the shots were fired. Oswald was arrested for the murder but shot dead before he could be tried.
In 1979 the US Congress House Select Committee on Assassinations said four shots could be heard on a tape recorded by a police motorcycle radio, and they appeared to come from two different locations.
The committee concluded that Oswald probably did not act alone. Cue conspiracy theories and feature films suggesting the murder was committed by more than one man.
WHERE IS THE ORIGINAL WORLD CUP?
The Jules Rimet trophy was named after the president of football's world governing body, FIFA, from 1921-1954.
Coveted worldwide, stolen in 1983
It was stolen in Brazil in 1983 after the soccer superpower won it permanently for their third World Cup success in 1970.
The trophy has never been recovered and many believe that thieves melted it down, fleeing Brazil with a replica.
WHO IS THE MINSTEAD RAPIST?
No-one knows for sure how many crimes this man has committed, but they have prompted the largest investigation of its kind ever mounted by the Metropolitan Police.
Since the early 1990s, he is suspected of having broken into the homes of more than 90 women aged between 68 and 88. Police say he is linked by semen and by patterns of behaviour to four rapes and about 30 other sexual assaults.
No match has yet been found on the UK's national DNA database.
WHERE IS SHERGAR'S BODY?
In February 1983, a year after finishing a glorious racing career, Shergar was snatched from the Aga Khan's Ballymany Stud in County Kildare, Ireland.
Shergar's value at stud was £10m
Conspiracy theories began about what had happened, with false reports of ransom demands and extracted sperm.
A police informer said the IRA had kidnapped Shergar to raise cash but had shot the thoroughbred when it panicked, hours after the kidnap.
There is still no conclusive proof of what happened to Shergar. A skull found in 2000 was not his.
THE FLOATING LIGHT BULB
American magician Harry Blackstone Jr is thought of as one of the greatest ever.
His 1977 version of the Floating Light Bulb, first performed by his father, is regarded by many magicians as perhaps the best illusion ever performed.
The lit bulb appeared to defy gravity by levitating above the audience.
There are modern versions of the trick, complete with instructions, but perhaps only Blackstone's widow Gay, who was also his assistant, knows exactly how he did it.
WHO DIES IN THE NEXT HARRY POTTER BOOK?
Speculation is growing after author JK Rowling confirmed that a key character would be killed in the next Harry Potter instalment.
Harry Potter and the Half-Blood Prince is due out in July and betting was suspended last week after a flurry of bets on Dumbledore aroused suspicion of a possible leak.
Actor Daniel Radcliffe, who plays Harry in the films, has said he suspects the young wizard may be killed off at some stage.
Any secret you would like to know the truth about? Let us know using the form below.
Is there a cure for the common cold that is withheld to promote the sale of cold/flu medicines that merely mask the effects?
Steven Jones, Liverpool, England
In the song, "You're so vain" by Carly Simon, when she sings, "You're so vain. I'll bet you think this song is about you." Who is she singing about?
Jim Lewis, Burlington, VT USA
Will there ever be an explanation for why otherwise sane and seemingly intelligent people watch soap operas?
Peter, Kingston, UK
Where is Radovan Karadzic? Where is Ratko Mladic?
Mark Green, Wimbledon, London
Is there really a metalic object concealed inside one of the twisted columns of Rosslin Chapel near Edinburgh, and has it been imaged / identified, and if so what does it appear to be?
Jack Howard, Leeds, UK
Did Shakespeare write all or any of his plays?
B Petlock, Washington, DC
Did Sibelius write an 8th symphony and is it buried with him ?
Jonathan Medtner, Seoul, Korea
Does Father Christmas really deliver all those presents in just one night?
Paul Trigger, Brighton
The voice behind the infamous "Yorkshire Ripper" tape. The real ripper was Peter Sutcliffe, a Yorkshireman. The voice on the tape had a Wearside accent. This led the investigation in the wrong direction.
Chas, Manchester, UK
Who killed the princes in the Tower? It seems clear that Richard was innocent - he had no motive, no 'previous' and was never accused at the time. Whereas Henry Tudor had the perfect motive and was an unscrupulous murderer. Richard was fingered by Thomas More, a good man but a Tudor propagandist - why do our history books perpetuate this slander? What is the true story?
Alan Chance, London
Who is buying the crazy frog song and why?
John Hunt, Ashford, Kent
What happened in Jesus' life from ages 12-30?
mase , SF California USA
I've seen information about a secretive so-called 'Majestic 12' group of influential people in the USA. Do they exist and, if so, who are they?
Roy Bailey, Crawley, UK
Is the sacred ark of the covenant in someone's private collection, and could the same apply to other important religious artefacts.
peter bishop, london
I would like conclusive proof regarding the supposed moon landings. It is strange given the huge advances in technology that nobody has been back during my lifetime. I had read that the Japanese were supposed to be building a telescope so powerful that it would be able to pick up sight of the lunar module left behind on the moon, assuming they ever went, as proof but have heard nothing further. I severely doubt man has yet walked on the moon but I'd like to know for certain.
Surely one of the biggest mysteries in UK history is the identity of Jack The Ripper?
Was he an aristocrat? A surgeon? Will we ever find out the truth or is all evidence now lost to father time?
Chris Martin, Milton Keynes
Did aliens ever land on this planet, in particular at Roswell.
Jon Hill, London
I would like to know the full version of the Third Secret of Our Lady of Fatima, given to the child seers in Fatima, Portugal in 1917. An apparently neutered version was released by the Vatican in 2000. The notes of one of the seers, Sister Lucia (who recently died) wrote the beginning of the Third Secret given by Our Lady as:- "In Portugal, the dogma of the Faith will always be retained, etc" When the so-called Third Secret was released by the Vatican in 2000, the "etc" written by Sr Lucia was never commented on or explained. A vision was described but no words were given. Why?
John Sheridan, Twickenham
Did Rudolf Hess fly to Scotland on a mission on behalf of Hitler, or was it just an act of madness?
Claudio Piombetti, Stanwell Moor, Surrey, UK
What came first the Chicken or the Egg?
What did happen to Hitler's body ?
Simon Bennett, London, UK
Was there a surviving member of the Russian royal family after the revolution?
Heather Stroud, Loughborough
What does F.A.B. stand for in Thunderbirds
Craig Vernon, Epping Essex
Does the NSA (National Security Agency) actually screen every telephone call made in the country for clues to potential security threats?
R. Dalton, Chicago, Ilinois, USA
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