If Saudi Arabia’s crown prince, Mohammed bin Salman, believes the sentencing to death of five hapless stooges for the murder of the dissident journalist, Jamal Khashoggi, is the end of the affair, he is sorely mistaken. The brutal killing at the Saudi consulate in Istanbul in October last year has shamed the kingdom, caused lasting harm to its global standing, and irretrievably damaged Prince Mohammed’s personal reputation.

In short, the whole business stinks – and the stench will not be dissipated, nor the noxious smell dispersed, by a travesty of a trial that bears little or no resemblance to a properly conducted legal proceeding. This horrendous crime will remain a gross and indelible mark on the conscience of the House of Saud.

The ponderous transactions of the criminal court in Riyadh, which handed down a total of eight guilty verdicts on Monday, lacked credibility from the outset. The trial was held in conditions of utmost secrecy throughout, further undermining confidence – and encouraging suspicions that the accused were dispensable fall guys.

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Those suspicions will only grow with confirmation that Prince Mohammed’s former senior adviser, Saud al-Qahtani, has been released without charge. The Saudi deputy public prosecutor, Shalaan bin Rajih Shalaan, previously said Qahtani had been involved in discussions about Khashoggi with the squad of agents that was sent to Istanbul.

The prosecutor said Qahtani had also acted in coordination with the Saudi deputy intelligence chief, Ahmed al-Asiri, who had ordered Khashoggi’s involuntary repatriation from Turkey. The suggestion was that members of the kidnap squad subsequently went “rogue” and killed Khashoggi without the consent of higher authority.

Both Qahtani and Asiri have been moved to other jobs. Asiri was put on trial but on Monday, Shalaan said he, too, had been released – due to insufficient evidence. Like Prince Mohammed, both men deny any personal responsibility for Khashoggi’s murder. In a television interview with CBS in September, Prince Mohammed said: “This was a heinous crime. But I take full responsibility as a leader in Saudi Arabia, especially since it was committed by individuals working for the Saudi government.” Asked whether he ordered the murder, Prince Mohammed replied: “Absolutely not.”

Profile Who was Jamal Khashoggi? Show Hide Jamal Khashoggi was one of the Arab world’s most prominent journalists and commentators. He was an outspoken critic of Saudi Arabia who dared to defy Crown Prince Mohammed bin Salman. While living in Saudi Arabia, Khashoggi was told to stop writing or posting on Twitter, where he had more than 1.6 million followers. He moved to the US in June 2017, where he continued to comment on his country both in print and on television. He wrote columns for the Washington Post and the Guardian.

His message struck a nuanced tone in the US, where he tried to acknowledge the reforms undertaken by Bin Salman while also highlighting the flaws. Khashoggi previously had close links with the Saudi royal family, including having served as a media aide to Prince Turki al-Faisal, when the latter was director general of the Saudi intelligence agency. He was also a former editor of the Saudi newspaper al-Watan and had worked with Prince Alwaleed bin Talal, a grandson of the first Saudi king. Khashoggi was murdered in the Saudi Arabian consulate in Istanbul in October 2018. Photograph: Virginia Mayo/AP

For eminent Saudi royal personages with face to save, this all looks very convenient. The regime will claim justice has been served and the guilty men identified and condemned. And consider this: the death sentences, barbaric in themselves, are preliminary. They may be appealed, commuted, or even dismissed at some future date when the world is no longer watching.

It all simply does not wash. A report published in June by the UN’s special rapporteur, whose independence and impartiality, unlike that of the Riyadh court, is not open to question, found “credible evidence” of liability for the murder among high-level Saudi officials, including the crown prince.

Play Video 1:14 UN special rapporteur condemns Jamal Khashoggi verdict as 'whitewash' – video

Khashoggi’s death was an extrajudicial killing and the investigation conducted by Saudi Arabia and Turkey failed to meet international standards, the rapporteur, Agnès Callamard, declared. She went on to allege that the Saudi authorities might still be engaged in obstructing justice – and demanded that the trial be suspended. The UN’s findings and recommendations were dismissed by Riyadh.

But Callamard was not alone in her suspicions. Indeed, the CIA, which has no particular reason to embarrass an important US Middle East ally and trading partner, went further. American officials expressed high confidence in a CIA finding last year that Prince Mohammed personally ordered the murder, a conclusion they said was supported by multiple sources. The agency reportedly pointed to the alleged involvement of Khalid bin Salman, Prince Mohammed’s brother who is the deputy defence minister. He was said to have “phoned Khashoggi, urged him to go to the Istanbul consulate, and assured him of safe conduct”. The Washington Post said it was unclear whether Khalid knew Khashoggi would be killed, but that he made the call at his brother’s direction.

Crown Prince Mohammed bin Salman. Photograph: Bandar Aljaloud Handout/EPA

One of the few people who appears to believe the official Saudi version of events is Donald Trump. Even if, privately, he does not, he has made it abundantly clear he will not allow the Khashoggi scandal to derail his own and Washington’s close relationship with the Saudis, which rests on arms and oil sales, mutual business interests and a shared antipathy to Iran. As in separate instances relating to Russia, Trump has effectively disowned his own intelligence community.

But if Prince Mohammed believes a corrupt poltroon in the White House can resurrect him and his ruined reputation, then once again, he is deluding himself. The murder has brought down the wrath of US Congress on his head where, as is the case in Britain and Europe, many continue to favour a halt to arms sales and possible post-Trump sanctions. It has shone an unforgiving light on broader, systemic human rights abuses by the Saudi regime. And it has drawn overdue attention to Riyadh’s murderous military campaign in Yemen.

The Khashoggi murder has forced the western democracies to question how much longer they can continue to pretend that Saudi Arabia, with its preening regal autocrats, gaping democratic deficit, and still largely unreformed, medieval attitude to women, is a normal country. Justice has not been done. Jamal Khashoggi, whose offence was to speak up freely and bravely against those who oppress and exploit his native land, has not been avenged.

Khashoggi’s true killers still await exposure and punishment. Whatever cover story the regime may propagate, the seeds of doubt have been sown. For Prince Mohammed and those of his blood, it may be a bitter harvest.

• Simon Tisdall is a foreign affairs commentator