KEY POINTS:
Two major investigations by French and British police concluded that Princess Diana's death in a Paris car crash was a tragic accident, but 10 years on many remain convinced she was murdered in a sinister plot.
The usual suspects cited by conspiracy theorists include the royal family - because they were unhappy Diana was to marry her lover, Muslim Dodi al-Fayed - or arms dealers, because they were angry at her support for a ban on landmines.
"They were killed as a result of a wicked conspiracy by people who did not want the princess to marry my son and were fearful of what she could say and do," Dodi's father Mohamed, the leading murder theory protagonist, told Reuters.
And there are some truly bizarre hypotheses.
These suggest leaders of a "new world order" assassinated her because she wouldn't marry former US President Bill Clinton, or that she was killed as part of a Satanic ritual, or even that she is still alive having faked her own death.
Alasdair Spark, at the Centre for Conspiracy Culture at the University of Winchester, said doubts about the official version of Diana's death reflected a common belief that the public were always deliberately misled by the authorities.
"At the heart of it is this very strong belief we are always lied to, that any government never tells you the truth," Spark told Reuters.
"People believe in conspiracy theories the way they believe in TV adverts. It's a very casual belief, sometimes it's more of a refusal to disbelieve. But people are prepared to entertain that it might be true," he said.
UNANSWERED DETAILS
One of the strengths of conspiracy theories is the focus on unanswered details, and arguments are developed from there.
In the case of Diana, much has been made of the untraced white Fiat Uno car that police reports say collided with the princess's car shortly before the fatal crash.
"If you get into a conversation with a conspiracy theorist, very, very quickly they'll be talking to you about the facts and details in exhaustive levels," Spark said.
"But at the same time actually often it's about the little inconsistent facts. Where is the white Uno? These sort of things, the piece of the jigsaw that doesn't fit, tend to get very exaggerated. You can spin fantasies out of that."
Spark said the internet had also played a crucial role in the spread of conspiracy ideas by allowing them to be easily disseminated. In the case of Diana, conspiracy theories were hitting websites within hours of her death.
And he said there was little authorities could do to convince those who believed in them. Despite the 832-page report by police, sceptics still doubt the official accounts on Diana.
JUDGMENT AFFECTED
Dr Karen Douglas, from the University of Kent, has carried out a study to assess how much people had been influenced by theories surrounding Diana's death.
She found that people exposed to Diana conspiracy theories were influenced by what they had been told when asked to rate how much they agreed with statements such as "Diana was killed by British secret agents".
The study also showed that they did not even realise that their judgment had been affected.
"If people aren't necessarily aware that these conspiracy theories are having an impact on their own attitude, they are much more likely to pass them on to other people. It might be some way in which they get perpetuated over time," she said.
Spark said the questions and doubts about Diana's death might reveal more about society itself than the crash.
"Is it really telling you about what happened in the late 1990s or is telling you about the state of Britain today, when people have become profoundly doubtful of government in the wake of the Iraq war?" he said.
The failure to find weapons of mass destruction in Iraq - the justification the government gave for the 2003 invasion - had fuelled doubts about official versions of events.
"Let's say you believe there's a conspiracy and you call for a public inquiry. The public inquiry results come out and people instantly pick it apart and say the public inquiry is part of the conspiracy. So it goes on and on, and on, and on."
- REUTERS
