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In the years since her Aug. 31, 1997, death in a Paris car crash, the tragic end of Diana Princess of Wales has remained an unfinished book, full of stray plotlines and conflicting accounts. But in recent months long-simmering questions—raised primarily by Mohamed Al Fayed, the father of Diana's boyfriend Dodi, who died with her in the fatal spinout of her black Mercedes S280 in Paris's Place de l'Alma tunnel—have been making front-page headlines in the British press. The reason: comments made earlier this year by Lord Stevens, chief investigator of the government probe into the deaths (known as Operation Paget), that the questions involved were "far more complex ... than any of us thought."

Does that mean, as Al Fayed has claimed, that Diana's and Dodi's deaths were orchestrated by Buckingham Palace? While Operation Paget's official findings will not be completed until later this year, this PEOPLE special report, based on interviews with several investigators involved with the probe, sorts out the many theories swirling around—and separates fact from fiction.

Was Diana Pregnant?

Rumors that Diana was carrying Dodi's child surfaced soon after her death—and were quickly denied by her friends. But Dodi's father has charged that Diana's embalming within hours was done to hinder a thorough postmortem exam. Investigators have taken this concern seriously enough that earlier this year they reinterviewed doctors at Paris's Pitié-Salpêtrière hospital, where Diana was taken after the crash.

Adding to the mystery, Diana looked to some as if she had the beginnings of a pregnancy tummy when she was photographed with Dodi just days before her death. From his yacht, on Aug. 28 and 29, five calls were made to Dodi's friends at a villa in Europe, including a call in which he "intimated the couple had wonderful news to share," an investigator says. Al Fayed claims to have "indisputable" proof that Diana was about nine weeks pregnant when she died. A member of Al Fayed's staff would say only "we are making our submissions to the appropriate authorities."

But, PEOPLE has learned, investigators have ruled out the pregnancy theory. "It is completely fictitious—without any foundation at all," one says. Bolstering their view: statements from two doctors from the French hospital who "knew exactly what state Diana was in, and she definitely was not pregnant," an investigator says.

WERE DIANA AND DODI ENGAGED?

Mohamed Al Fayed and other conspiracy theorists—who believe Diana was killed on orders from British intelligence—say an impending engagement could have been a motive. While the Palace never commented publicly on the relationship, Al Fayed has said he believes the House of Windsor was desperate to stop Diana from marrying and having children with Dodi, a Muslim.

One sign the relationship was taking a more serious turn: a $200,000 emerald-and-diamond ring (left) that Monte Carlo jeweler Alberto Repossi (above) has said he sold to Dodi. In a sworn statement to investigators, Repossi said he met with the couple in August in Saint-Tropez and measured Diana for the ring. "It was an engagement ring—Diana chose it herself, and Dodi picked it up from the shop the night before they died," Repossi told investigators.

Challenging that theory are some of Diana's friends, including Rosa Monckton, a former jewelry executive, who told a British newspaper that while the princess had mentioned a ring, she said that it was "going firmly on the fourth finger of my right hand"—not the traditional way to signal a betrothal.

Was Diana's Chauffeur a Secret Agent?

Henri Paul was behind the wheel of the black Mercedes S280 when it crashed into a cement pillar in the Place de l'Alma tunnel shortly after midnight on Aug. 31. Rumors about Paul's role in Diana's death have circulated since his body was pulled from the wreckage.

And now it turns out Paul was a spy. Last year, French authorities informed British investigators that the driver was on the payroll of the Directorate of Territorial Surveillance (DST), France's domestic intelligence service. Paul, who worked as deputy head of security at the Al Fayed-owned Ritz, had something any spy agency would want: a knowledge of the movements of diplomats and crime bosses. Skeptics like Ken Wharfe, Diana's former bodyguard, believe Paul's status doesn't mean Diana was murdered: "All major cities have agents working there and they will find informants at the hotel."

But puzzles remain. Chief among them: How had Paul, with a $35,000 salary, managed to stash away $160,000 in more than a dozen bank accounts—$120,000 of which was paid just before the crash, according to investigators? "The money trail is crucial in this case," one says, "and it's hotting up." While MI6, Britain's foreign-intelligence service, has not publicly commented on any involvement with Paul, investigators aren't dismissing theories that he may have been a patsy: "Henri Paul may well have received special instructions that night," one says. "It may be he only knew half of what was likely to happen. Paul was useful, but expendable."

Was Henri Paul Drunk at the Time of the Crash?

Yes—according to French police, the day after the crash when they reported that Paul's blood-alcohol levels were triple the legal limit and that his blood had trace amounts of antidepressant and antipsychotic drugs. Al Fayed charged that Paul's blood samples had been deliberately swapped at the morgue with those of a suicide victim. In a stunning report, British investigators say that French authorities have acknowledged an unspecified error with the blood samples, but stand by their conclusion that Paul was drunk. Chief British investigator Lord Stevens continues to believe the crash was an accident, a leading London-based criminal lawyer close to the investigation says.

WERE SECRET AGENTS SPYING ON DIANA?

As a royal traveling abroad, Diana may have been watched—for her own protection—by agents from MI6, Britain's secret intelligence service, says a source close to the investigation. As part of his murder plot claim, Mohamed Al Fayed has charged that in the days after the crash, MI6 dispatched a team of operatives to cover the tracks of its agents working on the night of Diana's death.

Fueling speculation was the arrest in late 2005 in Cyprus of a shadowy figure known as Agent Y, a British operative who was accused of torturing terrorist suspects in Greece. Soon after, according to a lawyer for Mohamed Al Fayed, an informant told investigators that Agent Y had been part of a cell assigned to block inquiries into MI6 operations involving Diana. That explosive charge prompted investigators to reinterview dozens of secret agents who were operating in Paris the night Diana died.

Was Diana's Body Embalmed?

One lingering mystery surrounds the reported embalming of Diana's body just hours after she died. The procedure would have violated a French law against embalming a body that is to undergo an autopsy. Some close to the case believe that whoever might have ordered the procedure—only partially completed—did so with the intention that the powerful preservative formaldehyde might throw off tests that could detect a pregnancy.

So who supposedly gave the order? Dominique Lecomte, the French pathologist who did the autopsy, isn't talking. Some French legal sources have told investigators that the word came down from Sir Michael Jay, Britain's ambassador in France at the time, possibly at the urging of higher-ups. The investigation has gone all the way up to Prince Charles, who, investigators say, in a December interview with Lord Stevens denied involvement. Jay, now head of Britain's diplomatic service, has also denied the allegations.

Whoever may have ordered it, could embalming have hidden a pregnancy? Medical experts say no.

Former royal coroner Dr. John Burton—who attended the examination of Diana's and Dodi's bodies—has said that the procedure "wouldn't interfere in any way with a pathologist's ability to carry out a postmortem."

WHAT DO WILLIAM AND HARRY THINK HAPPENED THAT NIGHT?

The princes, just 15 and 12 at the time, were vacationing at the Queen's Balmoral estate in Scotland when Diana died. "They never speak about it to their friends, and those friends don't raise it with them," says a chum. "It would be crass." Sources close to the royal family believe the princes have always blamed the paparazzi—not secret agents or other shadowy figures—for their mother's death. Still, William, now 23, and Harry, 21, can't help but be affected by the media maelstrom that seemingly has no end. "They are sensitive young men," says one friend. "They feel a prick of pain when these stories come up. They simply miss their mum."

  • Contributors:
  • Reported by Peter Allen/Paris,
  • Mary Papenfuss/Paris,
  • Simon Perry/London,
  • Ellen Tumposky/London.