The coroner, Lord Justice Scott Baker, is expected to begin his summation Monday, which may take days before going to the jury.
The key question for the jurors is whether the car crash in a Paris road tunnel on Aug. 31, 1997 was an accident.
Mohamed Al Fayed has not budged from claiming that his son and the princess died at the hands of British security agents, acting at Prince Philip's behest.
French police concluded it was an accident, caused in part by speeding and by the high alcohol level in driver Henri Paul's blood. A British police investigation concurred.
More than 240 witnesses have testified since the inquest began on Oct. 2, including Diana's close friends and former butler, Philip's private secretary and a former head of the Secret Intelligence Service, MI6. Al Fayed's late bid to force the coroner to summon Philip to testify, and for written questions to be put to the queen, was summarily rejected by a higher court.
There has been evidence that Diana feared dying in a car crash, but that she also had speculated about death in a helicopter or airplane crash; there was testimony that she feared Philip.
The basic scene is familiar: the couple's car slammed into a concrete pillar in the Alma tunnel, after apparently having a glancing collision with a white Fiat Uno, as they were pursued from the Ritz Hotel by photographers. Some witnesses said they saw flashes of light in the instant before the crash; other witnesses didn't notice any. Al Fayed's claim is that flashing lights disoriented the driver and sent the couple's car into a fatal skid.
But there was precious little evidence to back up his claims that his son and Diana were engaged, that she was pregnant and that Philip was at the head of a murder plot.
Al Fayed believes the Establishment simply didn't want Diana to marry his son, a Muslim.
Al Fayed worked his way up from a humble birth in Alexandria, Egypt, in 1929 to become one of the richest men in Britain. He owns Harrods department store, a Scottish castle, the Fulham FC soccer team and the Ritz Hotel.
As the inquest unfolded, some distance opened between Al Fayed and his lawyers.
Michael Mansfield, his main advocate, steered away from accusing Philip or claiming MI6 assassinated the couple. He did suggest that rogue agents might have been involved.
"Mr. Al Fayed ... has certain beliefs which he has made clear. He is plainly not a member of MI6 or, certainly, the Establishment either," Mansfield told the coroner.
"I have never at any stage withdrawn any of his beliefs but you will see I have focused very carefully on elements of what he is suggesting that may be true; in other words, for which there is, forensically, evidence to support his beliefs."
Mansfield has suggested that Diana's campaign against land mines was the motive for the conspiracy - that she was assembling a dossier "capable of exposing historically British involvement in Angola because of who manufactured the weaponry, how it was got in there."
When he testified on Feb. 18, Al Fayed affirmed his belief that the conspirators included Prince Philip; Diana's ex-husband, Prince Charles; Tony Blair, who was prime minister when she died; Diana's sister, Sarah McCorquodale; her brother-in-law, Robert Fellowes; two former chiefs of London police; driver Paul; the CIA; Diana's attorney, the late Lord Mishcon; two French toxicologists; Britain's ambassador to France; members of the French medical service; and three bodyguards Al Fayed once employed.
Al Fayed has claimed Fellowes was in Paris on the night of the crash sending messages to agents back in Britain. But none of Al Fayed's lawyers put that to Fellowes when he testified.
Al Fayed was the only witness to claim Diana was engaged to his son. He was told of the engagement, Al Fayed said, in a telephone call hours before the crash.
He alone definitively asserted that Diana was pregnant. The pathologist who examined her body said he saw no evidence, and others testified she was conscientious about taking her birth control pills.
So where was the proof? Al Fayed was asked.
"How can you want me to get the proof?" he said. "I am facing a steel wall of the security service, Official Secrets Act."
The coroner asked Al Fayed if he could possibly be wrong.
"No way, 100 percent," Al Fayed said. "I am certain. I am the father who lost his son. And I know exactly the situations. I know exactly the facts."