The file on Judge Herve Stephan's desk in Paris is more than 30 centimetres high and still growing. A year after a car crash which shocked the world investigators are still battling to separate fact from conspiracy theory to find out who was responsible for the death of Diana Princess of Wales and her lover Dodi Fayed. Senior British police officers have claimed it is the sort of investigation that could have been wrapped up by a good road traffic sergeant in eight weeks. But a quick result was never an option in an inquiry that, whatever its findings, will attract amateur theories for decades to come. There is still no exact explanation as to why the black Mercedes 280S crashed in the way it did. But an apparent reluctance by some to accept the simple fact this could have been just another drink driving accident has led the inquiry to drag on with fresh allegations being made almost every week. The author of many of these allegations has been Dodi's father, the Egyptian millionaire Mohamed Al Fayed, who has employed his own team of detectives and come up with an ever-changing list of suspects. Only this week, in an astonishing about-turn from his earlier claims, the Harrods owner blamed his own bodyguard Trevor Rees-Jones, 30, and his colleague Kes Wingfield, 33, for causing the accident through incompetence and unprofessional practices. It is the third time Mr Fayed has changed his mind about who was responsible for the crash. Initially he blamed the paparazzi for pursuing the black Mercedes carrying his son and Princess Diana from the Ritz Hotel and forcing the driver to take evasive action. When the press were found to have been a significant distance away from the car before it collided with a concrete pillar in the Place de l'Alma underpass, Mr Fayed turned his attacks on the British establishment and claimed he was '99.5 per cent certain' the couple's death had been the result of a bizarre conspiracy. 'This was not an accident. There was a conspiracy . . . I believe there were people who did not want Diana and Dodi to be together,' he told the British press earlier this year. But now Mr Fayed has claimed the bodyguards are responsible for not insisting on a back-up car and allowing the driver, Henri Paul to take an indirect route. Mr Fayed's spokesman, Laurie Mayer, insisted there was no contradiction in these different explanations for the accident on September 31, last year. 'The fact of the matter is we don't regard any one of these things as being mutually exclusive,' Mr Mayer said. 'It was a complicated accident, there were all kinds of factors and the conduct of the bodyguards was inevitably a contributing factor. All he [Mr Fayed] is saying is that if they had carried out the established procedures the tragedy might have been averted.' Mr Rees-Jones's lawyers have hinted they believed Mr Fayed's latest accusation was because they had asked the French investigating magistrate to interview two senior Ritz Hotel employees with a view to possible legal action for damages against them. 'The proper thing for Mr Fayed to do would be to go to the judge and say he thinks the bodyguards let him down, if he does indeed think that. The problem he would have with that is the judge is very likely to ask why he had not been told this before,' Mr Rees-Jones' lawyer David Crawford said. Officials in Paris have revealed little detail on the progress of the investigation, which by convention is being conducted in secret. But a statement from the prosecutor's office explained the length of the inquiry was a result of 'the context of this affair and its international importance'. Not least of the delays has been the need to examine all the submissions made by conspiracy theorists. All reports made to the inquiry had been carefully scrutinised 'including the many that were proved to be impossible or fantastical', the statement said in part. But privately, Paris-based officials admit the undercurrent of fresh allegations from the United Kingdom was not helping the inquiry reach a conclusion. 'It is a criminal investigation so in the French system we cannot comment, but there have been delays and there have been some things which have not moved as smoothly as we would hope,' one official said. The 24-strong inquiry team has already compiled more than 5,000 pages of evidence and taken statements from 300 witnesses in an investigation bogged down by bureaucracy. Police inquiries into the case labelled 'Accident Mortel de la Circulation Date 31/8/97 heure 00h30' began even before the couple were officially declared dead. At 20 minutes past midnight on August 31 they had finished dinner at the Ritz Hotel, owned by Mr Fayed, and decided to depart from normal security procedures to escape photographers who had dogged them all evening. Dodi Fayed decided to use a hotel limousine to take them to his flat on the Champs Elysees. A member of the Ritz's security team, Paul, was paged to act as their driver; while Mr Wingfield was told to drive off in another car as a decoy. The two English bodyguards say they argued against the idea but were told by Princess Diana's boyfriend he had phoned his father who had approved the plan. Earlier that day a hotel driver had reported the Mercedes' brake light was not working though no action had apparently been taken to address the problem. An earlier chauffeur had also reported the car tended to drift to the left at the rear if the brakes were applied too hard. The couple climbed into the back of the armoured limousine while Mr Rees- Jones sat in the front next to the driver and the Mercedes sped off leaving the paparazzi behind. Apparently in an effort to shake off the pursuing photographers Paul took a less direct route to Dodi Fayed's flat through the Place de la Concorde and on to the fast dual carriageway along the banks of the Seine. Five minutes later the Mercedes - travelling at an estimated 130-160 kph - entered the ramp down to the tunnel under the Place de l'Alma. No one can be sure what happened next but for some reason the car skidded out of control and hit the parapet between the two carriageways. As it rebounded into the road the driver seems to have struggled to control the car, even hitting the accelerator to increase the vehicle's grip on the road. But still travelling at speed the Mercedes veered to the left, smashed into the 13th pillar of the underpass and spun round to face the way it had come. The force of the impact killed Dodi Fayed and Paul instantly and left Mr Rees-Jones, the only person in the car wearing a seat belt, with terrible injuries to his face and back. Princess Diana was taken to the Pitie Salpetriere Hospital suffering internal bleeding, concussion, a broken arm and cuts to one thigh. She was declared dead at 4am Sunday morning after going into cardiac arrest. Chief Superintendent Martine Monteil, France's highest ranking woman police officer, was placed in charge of the investigation that quickly established the car's 41-year-old driver had more than three times the legal amount of alcohol in his blood. He had also been prescribed four different kinds of drugs including Prozac, intended to combat depression or alcoholism. None of these drugs are supposed to be taken with alcohol. He was also found not to have the necessary permit required in France to drive VIPs in heavy, high-powered limousines. In the days after the accident the inquiry focused firmly on the pursuing photographers; eight of whom, together with a motorcyclist, are still facing charges of manslaughter and failure to assist victims at the scene of an accident. But investigators have since dismissed the claims the paparazzi were responsible for the accident and have switched their attention to the driver of a mysterious white Fiat Uno seen emerging from the underpass immediately after the accident. The remains of the Mercedes are still being examined 12 months after the incident, with special attention being paid to long white grazes on the limousine's right front wing, apparently caused by collision with the Fiat. But the inquiry has failed to track down the unknown vehicle amongst the 40,000 white Fiat Unos registered in Paris. Further criticism was levelled against the investigators in June when they refused to hold a full reconstruction of the journey taken by the Mercedes from the Ritz Hotel. The plan was blocked because of Judge Stephan's fears it could cause major congestion in Paris while it was crowded with World Cup football fans. Much hope had been pinned on Mr Rees-Jones being able to give an account of what happened in the Mercedes as it went into the underpass, and who gave instructions for Paul to take the route he did and to drive at such speed. But his injuries have meant he has been able to remember little about the events of that night after leaving the Ritz Hotel. As the inquiry enters what those involved hope will be its final stage, investigation is switching to the management of the Ritz Hotel and how much they knew about Paul's drinking habits and his use of tranquillisers. Earlier this week prosecutors interviewed the hotel's manager Frank Klein, and the assistant manager, Claude Roulet, who was in charge of the hotel on the night of the accident. Management of the company that hired the Mercedes to the hotel might also face questioning. It is accepted Dodi Fayed only decided to use the Mercedes minutes before the couple left the hotel and that Paul selected the roundabout route to the Champs Elysees at the last minute. But many will continue to believe the white Fiat was somehow deliberately lying in wait for the couple as they sped through the underpass. Even when the file on Judge Stephan's desk is closed there are many who will continue the investigation.