Some time ago Christopher Hitchens disinterred an aperçu of Conor Cruise O’Brien that ‘intellectuals who were too fastidious to sacrifice civility and objectivity for the revolution could quite often be induced to make these very sacrifices for the counter-revolution’. A similar trait can be observed among the panjandrums of American publishing. Although they make a lot of noise about freedom of speech, they nevertheless set impossibly high thresholds of authentication before anyone seeking to advance a conspiracy theory, but lay down a welcome mat for authors of emollient rebuttals.

Thus, from the presses of Random House in 1993 came Gerald Posner’s Case Closed (Oswald did it), and last year from Little, Brown, Norman Mailer’s Oswald’s Tale (Lee acted alone). Meanwhile, the doyen of the Warren Commission’s critics, Mark Lane, can only get published by a one-Apple Mac outfit in the boondocks.

As with Jack’s assassination, so, largely, with Bobby’s. At least, until now, it seems. Here we have no less a house than W W Norton issuing a book about the RFK killing by an author whose previous work includes How Crime Influences Professional Football and Ronald Reagan, MCA and the Mob. Maybe now, at last, the respectable book-buying public will be indoctrinated into secrets hitherto vouchsafed only to a few bearded men on the wilder shores of the Internet.

First, the official version. Just ten or eleven minutes after 12.00am on 5 June 1968 Robert Kennedy left the ballroom of the Ambassador Hotel in Los Angeles, where he had been celebrating his victory in California’s Democratic primary. To get to a scheduled press conference in the Colonial Room he had to pass through a pantry. Waiting there were a number of supporters who wanted to shake his hand and wish him God’s speed to the White House. Also waiting was Sirhan Bishara Sirhan, a twenty-four-year-old former stable lad and apprentice jockey. According to numerous witnesses at the scene, a number of shots rang out as Kennedy’s party entered the pantry. Six people fell wounded, among them Kennedy, who was later to die in hospital. Amidst the general chaos, Sirhan Sirhan was spotted holding an Iver Johnson .22 calibre revolver and was overpowered, disarmed and held until the police arrived.

It was subsequently discovered that Sirhan had spent the previous day at the San Gabriel Valley Gun Club firing an Iver Johnson .22 and that bullets from just such a gun had caused the politician’s fatal wounds. At Sirhan’s home the police found an envelope on which was written ‘Robert Fitzgerald [sic] Kennedy must soon die.’ Also they turned up a number of notebooks which appeared to incriminate Sirhan in the assassination of Robert Francis Kennedy, all in the suspect’s own hand.

So, case closed, then? Not exactly. Sirhan has denied culpability, claiming to have no recollection at all of the events of the 5th of June. Moreover, numerous inconsistencies have been discovered both in the scientific evidence and in the police records of the investigation which powerfully suggest a conspiracy. Dan Moldea finds even more.

First, there is the matter of the woman in the polka-dot dress. Within a few minutes of the shooting Sergeant Paul Sharaga, a policeman on duty outside the hotel, was approached by an elderly couple who told him that a young man and a woman, the latter in a polka-dot dress, had run past them laughing and shouting out: ‘We shot him. We shot Kennedy.’ Sharaga radioed the report to base and put out an alert. He noted when and how many times he did this, but either his calls were not properly logged by the LAPD, or the logs were subsequently altered. Later, Sharaga’s report in the LAPD files was shown to have been rewritten or ‘sanitised’ without his knowledge. A third person who claimed to have encountered the woman in the polka-dot dress was shouted at and hectored by her polygraph operator (she really was – Moldea has the tape); she became so nervous she failed the lie-detector test.

Then there is the question of how many shots were fired. Six people were wounded, Kennedy receiving at least three bullets. FBI crime-scene reports appear to show extra bullet holes in a wooden door frame and in the pantry roof. Sirhan’s gun held eight rounds. He never reloaded. The shot that killed Kennedy was fired, as powder burns show, from a range of no more than one or two inches. Yet no witness puts Sirhan closer than two feet from his supposed victim. Were there, therefore, two gunmen? The gun and much of the raw ballistics evidence curiously disappeared after the trial. The more Moldea digs, the more unsatisfactory the official version seems.

One theory the author does not buy, though, is the Manchurian Candidate theory, which propose that Sirhan was, like the protagonist in John Frankenheimer’s film, brainwashed, programmed or hypnotised into playing some part in the slaying and then forgetting about it later. Many serious people have believed this, though, including the psychiatrist at San Quentin prison.

At a later stage in his investigation Moldea is granted a meeting with Sirhan. Suddenly, as they talk, the author is struck by the realisation that Sirhan’s various blackouts and memory lapses are neither general nor random. In fact, they very precisely correlate with legal technicalities touching upon premeditation and guilt. He has spotted the convict’s game – preparing for a parole hearing due this year.

No sooner have the prison gates closed behind him than Moldea, in just a few pages, demolishes the house of cards he has so painstakingly built. The inconsistencies in the scientific evidence are brushed aside with a casual hand; people have clearly mistaken or misremembered what they saw. What of the little matter of the range at which the fatal shot was fired? Well, Kennedy must have fallen forward after the first shot, bringing his neck closer to Sirhan’s gun. And the woman in the polka-dot dress? She must have said ‘They’ve shot Kennedy’, not ‘We’ve shot Kennedy’. And why was she so happy? Maybe she was a Republican.

We are back in the realm of double standards. Moldea, who has insisted on applying the very highest standards of corroboration while building up the conspiracy theory, is strangely content in retiring from it to rely upon little more than gut feelings and plain old common sense. And yet, so well does he write about his encounter with Sirhan that you feel his intuitions are sound. But even if Sirhan Sirhan did act alone, it is not the conspiracy buffs who are left looking foolish at the end of Moldea’s book but the authorities whose bungling, cover-ups, lies and evasions have until now made a conspiracy so plausible. And let’s not forget the smarty-pants New York editors who may consistently have believed the right thing, but did so for all the wrong reasons.