Britain's royal coroner asked police to look into theories a conspiracy led to the car crash in Paris that killed Princess Diana (search) and boyfriend Dodi Fayed (search), saying Tuesday he was obliged "to separate fact from fiction and speculation."

Coroner Michael Burgess' request -- part of the opening of official inquests into their 1997 deaths -- came as a tabloid newspaper reported Diana believed Prince Charles (search) was plotting to kill her by staging a car accident. Fayed's father said he suspects not only Charles, but also his father, Prince Philip (search).

A French investigation found the crash was an accident and that driver Henri Paul, who also died, had been drinking. But more sinister explanations for the crash abound, and Burgess said he asked police to investigate whether he should take them up in his inquests.

"I'm aware that there is speculation that these deaths were not the result of a sad but relatively straightforward road traffic accident in Paris," Burgess said.

"I have asked the Metropolitan Police Commissioner [Sir John Stevens] to make inquiries. The results of these inquiries will help me to decide whether such matters will fall within the scope of the investigation carried out at the inquests," he said.

The coroner immediately adjourned his long-awaited inquiry -- Britain's first investigation of the crash -- for at least a year to 15 months, saying he needs that time to review evidence gathered by French authorities and conduct his own investigations.

He acknowledged that "it would have been desirable for these inquests to have been heard and completed long ago." That was impossible because he must rely heavily on French evidence that will not be available to him until all legal proceedings springing from the case there are finished, he said.

Burgess said he expects the French proceedings to wind down soon but warned that any unexpected delay could further slow his work. An appeal by French prosecutors is still pending against the November acquittal of three photographers whom Fayed's father accused of invading his son's privacy by taking pictures at the crash scene.

France's highest court dropped manslaughter charges in 2002 against nine photographers who pursued the car before it crashed or who took photos at the site.

On Tuesday, the Daily Mirror tabloid reported that Diana, in a letter to her butler Paul Burrell, claimed her ex-husband "is planning 'an accident' in my car, brake failure and serious head injury in order to make the path clear for him to marry" his longtime girlfriend Camilla Parker Bowles.

Charles' office said it would not comment on the charge. Sarah Ferguson, the Duchess of York, told FOX News Channel's "FOX & Friends" that the report was "disgraceful" and "absolutely outrageous."

The paper reported the letter in October but did not originally identify Charles as the person Diana suspected.

Egyptian-born billionaire Mohammed al Fayed, Dodi Fayed's father, reiterated his belief that Diana, 36, and his 42-year-old son were victims of a plot and said he thought Charles and his father, Prince Philip, were involved.

"It's absolute black and white, horrendous murder," al Fayed told reporters at the formal opening of the separate inquest into his son's death in Reigate, outside London, hours after Burgess opened the Diana inquiry.

"It's the head of the royal family and I suspect not only Prince Charles" but also Queen Elizabeth II's husband, Philip, whom he described as "racist at the core." Al Fayed has in the past said Philip plotted against Diana because the royal family objected to her relationship with a Muslim.

The palace dismisses such charges.

Al Fayed, who owns Harrods department store, has campaigned for a full public inquiry into the deaths and had said a coroner's inquest was too narrow.

But Diana's former bodyguard Ken Wharfe dismissed the possibility that she was murdered.

"I have said this many, many times: the Princess of Wales was killed tragically in nothing more than a mundane road traffic accident," he told ITV television.

"If we look at the conspiracy theories perpetrated by Mohammed al Fayed again, you look at the evidence, there is no evidence here. It is mere speculation," Wharfe said.

Burgess said he would focus his investigation on several key questions -- "how, when and where the cause of death arose."

He said he would also "have to consider whether there is any other possible source of evidence or line of inquiry which may be relevant and which needs to be addressed, even if only to exclude it as not being relevant thereafter."

There have been unsubstantiated stories of photographs of the crash site being stolen, of Diana being pregnant, suspicion about closed-circuit television cameras inside the tunnel where the crash occurred that were said to have been turned to face a wall, and claims that Diana could have been saved if she had reached a hospital more quickly.

In its Wednesday editions, The Times of London quoted John Burton, who was the coroner for the Queen's Household when Diana died, that a post-mortem examination in London on Aug. 31, 1997, showed she was not pregnant. "I was actually present when she was examined" by a Home office pathologist. "She wasn't pregnant," Burton was quoted as saying.

Clarence House, Charles' official residence, said he and his sons, Princes William and Harry, "are very pleased that the inquest is finally under way." They did not attend the formal opening.

One of Diana's sisters, Lady Sarah McQuorquodale, did attend.