A defiant Mohammed al Fayed on Thursday rejected a government report that ruled the deaths of his son Dodi and Princess Diana were accidents, clinging to the belief their deaths were the result of a royal conspiracy.

"I'm certain 100 percent that a leading member of the royal family has planned that and that the whole plot was executed on his order with the help of members of MI6," Al Fayed said at a press conference following the release of the report.

The billionaire Harrods department store owner went on to call Lord John Stevens, the former chief of the Metropolitan Police who led the investigation, a "tool for the establishment and the Royal Family and intelligence."

Al Fayed vowed to expose the truth even if it cost him his last penny.

"God will help me, I'm sure, and with God's blessing I will uncover and show the whole world and this country that they have terrorists that come and execute any crime with their power in government and high places in the royal family, they can cover up anything and they think that the public can be duped," he said.

The British police inquiry, which took three years to compile, concluded that the deaths of Dodi al Fayed, 42, and Princess Diana, 36, were a "tragic accident."

Click here to read the report.

The couple was killed along with chauffeur Henri Paul when their Mercedes crashed in the Pont d'Alma tunnel in Paris on Aug. 31, 1997, while being chased by media photographers.

Paul was drunk, with a blood-alcohol level twice the British legal limit, and driving at twice the local speed limit before the crash, Stevens said.

"We can say with certainty that the car hit the curb just before the 13th pillar of the central reservation in the Alma underpass, at a speed of 61 to 63 miles per hour," Stevens said in presenting the report. "Nothing in the very rapid sequence of events we have reconstructed supports the allegation of conspiracy to murder."

Stevens said that photographers had prompted Diana and al Fayed to change travel plans before their death. Contradicting longstanding rumors, family and friends denied in interviews that Diana was about to marry al Fayed, and Diana was not pregnant, Stevens said.

"From the evidence of her close friends and associates, she was not engaged and not about to get engaged," Stevens said.

Stevens said he had interviewed Prince Charles, Diana's former husband, and had communicated with Philip and her elder son, Prince William.

"I have seen nothing that would justify further enquiries with any member of the royal family," he said.

He said William had said that there had been no indication that Diana was about to get married again.

Al Fayed's spokesman, Michael Cole, accused police of jeopardizing the impartiality of the upcoming coroner's inquest by leaking details of their investigation.

Cole said it was "highly unsatisfactory" that up to 18 key witnesses to the crash were not interviewed by the police.

He called for next year's inquests into the deaths to be heard before a jury so that the evidence presented by Lord Stevens could be "thoroughly tested".

Diana's sons endorsed the findings. Princes William and Harry "trust that these conclusive findings will end the speculation surrounding the death of their mother Diana, Princess of Wales," according to a statement from Clarence House, their father's office.

Earl Spencer, Diana's brother, and her sisters Lady Sarah McCorquodale and Lady Jane Fellowes, also supported Stevens' findings.

"We have been briefed on the conclusions of the inquiry and agree with them entirely, and look forward to reading the full report in detail," their statement said.

Rumors and conspiracy theories continue to swirl around Diana's death, despite a French judge's 1999 ruling that the crash was an accident.

A poll commissioned by the BBC, released earlier this month, found that 31 percent of the sample believed the deaths were not an accident, while 43 percent believed they were. The poll of 1,000 adults had a margin of error of 3 percentage points.

The British inquiry, which involved 15 police personnel and is estimated to have cost millions of dollars, used cutting-edge computer technology to reconstruct the crash scene in three dimensions, and examined the wrecked Mercedes in painstaking detail. Stevens looked at hundreds of witness statements and traveled to Paris to see the site of the crash.

Stevens also said U.S. officials had assured him that secretly recorded conversations in their possession shed no new light on her death.

The U.S. National Security Agency said Tuesday it had never targeted Diana's communications, but acknowledged it had 39 classified documents containing references to the princess.

The publication of Stevens' report will allow an inquest into Diana's death finally to get under way.

The inquest, convened and then swiftly adjourned in 2004, is due to formally resume next year under a retired senior judge, Dame Elizabeth Butler-Sloss. Preliminary hearings will be held Jan. 8-9 at the Royal Courts of Justice.

The Associated Press contributed to this report.