He has spent the last six years looking into the circumstances around the death of Princess Diana, and has written extensively on the subject, as well as producing a previous documentary.
Gregory also has a new book about the last days of Princess Diana coming out in the summer, entitled, "Diana: The Last Days."
Gregory set out to look at the possible motives for murder and found that the more he has delved into Diana and Dodi's death, the less evidence he finds to support conspiracy theories.
He basically looks at each of the questions that have been raised by the event and finds nothing to support any of the conspiracy theories.
For one, Gregory tells The Early Show co-anchor Hannah Storm, Henry Paul, the man who drove the limo that fateful day was completely drunk.
He says, "I found out that the French didn't just accept the first results. They did second and third tests. And, in fact, the most important thing I found in my research was pictures of his corpse in the morgue. And a message from the judge, which was signed by him and by his client saying, 'We were here.' We did a second set of samples. Any idea they got the wrong body or the wrong blood samples is completely wrong."
Gregory points out that Mohamed al Fayed has been talking up conspiracy theories to absolve his own guilt, because he gave his blessing to Dodi and Diana leaving al Fayed's hotel that night, using an al Fayed driver.
He says, "It's a blame deflection strategy because every minute that the world thinks about something other than it was the al Fayed's fault is good for him. But the reality is that Princess Diana on her last journey was traveling from Mr. al Fayed's hotel the Ritz, into one of his apartments in one of his cars with his driver and with his son. And what we have found out, in this documentary, is that Mohamed al Fayed, personally gave permission for all of this to happen on the phone to Dodi. As a result, Dodi and Princess Diana left by the back door with the unqualified Henri Paul, who later turned out to be drunk, and they left two fully qualified chauffeurs outside the front door of the Ritz."
Gregory has seen the entire French report on the crash, and knows that the British coroner will be using the French investigation as the basis for his inquest. But he has engaged Britain's most senior policeman (Sir John Stephens) to rule out any other possible cause of the crash. Witnesses were telling the same story: the Fiat Uno brushed the Mercedes, but did not cause the crash.
Those who have been looking for some sort of motive for the royal family to possibly eliminate Diana have pointed to the fact that they believe she was pregnant. But the mortuary manager Gregory interviews for the first time on British television says conclusively that Diana was not pregnant.
He says, "We found out from talking to an eyewitness at the inquest that she was not pregnant. We spoke to the mortuary manager Robert Thompson. And he was standing right next to the pathologist, Robert Chandler, I think his name is. And as the pathologist divided the princess's uterus, which is standard procedure in any autopsy, he remarked, 'Oh, well, she wasn't pregnant.' I asked him, 'is that in the autopsy report?' and he said, 'yes.' So we know when the coroner continues with his inquest, he will find that she was certainly not pregnant. It's just a cruel lie to suggest that she was pregnant because she had only known Dodi for five weeks. She had just had her period. We found out that from her best friend who was on holiday with her in the ten days before she died."
Gregory further concludes in the documentary that Diana was not engaged to Dodi al Fayed, and wasn't going to live with him.
As for the theories that the French ambulance service was very slow and culpable in her death, Gregory says, "We found out after the crash, immediately after the crash, as they were transferring her from the Mercedes to the ambulance, she had a heart attack. As a result, the paramedics, who were there had to save her life first. Otherwise, there wouldn't have been any point in putting her in the ambulance. It took quite a long time to save her life from the first heart attack and then stabilize her. As a result, they had to drive very, very slowly to the hospital, because she had low blood pressure. And, therefore, criticism of the French emergency service is completely unfounded. In our documentary we talk to the head of the Samu ambulance brigade and he says what happened and we have eyewitness accounts from some of the medics."
It is expected for Prince Charles to be interviewed as part of the British investigation into the letter Diana wrote several months before she died. But Gregory says, "I don't think Prince Charles or the royal family have got anything whatsoever to do with Princess Diana's death. And I'm quite convinced, having seen the evidence myself, that the coroner will not find that it was anything other than a tragic car accident. But the reason we made our film was to dispel a lot of the myths that continue to circulate around what was a tragic, drunken car accident."