Amid the doubt and scepticism, an independent investigation into the Khashoggi affair is now essential

At first glance, the agreement between Turkey and Saudi Arabia about a search of the Saudi consulate in Istanbul by the Turkish authorities looks like progress. It comes after a telephone conversation between the king of Saudi Arabia and the president of Turkey, an appropriately high-level exchange, given the global revulsion at the story. The Saudis have also promised an “internal” investigation into events at their diplomatic outpost, the place where, it is widely thought, the dissident journalist Jamal Khashoggi met his end.

Yet the scope for a whitewash – real or perceived – by two regimes looking for some sort of accommodation is plain. It is, therefore, not good enough. What is needed is some form of thorough independent international investigation to find out the truth about what happened.

There are rumours about a botched rendition, for example, about Mr Khashoggi’s body being dismembered and flown under diplomatic cover to Saudi Arabia, about the bugging of the consulate by the Turkish authorities, and about how much or how little was known about the incident on the part of the powerful Saudi crown prince, Mohammed bin Salman.

There are plenty of theories. An independent international investigation, probably under the auspices of the United Nations, has a better chance than anything so far suggested of satisfying angry international opinion. In its absence, the speculation will pile up, and the Saudis will be doomed to issue ever more vehement denials that are treated with scepticism if not contempt by the wider world. They may have thought they had a problem with Mr Khashoggi; his death presents them with a much more intractable one.

Even from Donald Trump there is talk of sanctions, though, pointedly, he refused to include major arms deals among the steps he is prepared to take to “punish” Saudi Arabia. It is a remarkable moment, though, when an American Republican president is prepared to talk about Saudi Arabia in such terms, given the long-term strategic alliance between the two nations. It is even stranger to find Washington preparing to impose sanctions and public criticism simultaneously on Saudi Arabia and Iran.

Mr Trump suggests that there are measures other than an arms embargo that could be taken. As with Russia, the expulsion of diplomats might be one course. In any event, if they could but see it, it would be in Saudi Arabia’s own interests to collaborate fully with an investigation into Mr Khashoggi’s disappearance before matters escalate further.

Gradually sanctions could come and they could bite. Saudi Arabia is still rich, but the oil price is not as high as they might wish, and their efforts to provide for an alternative long-term economic future to oil and living off the dividends from their sovereign wealth fund have yet to materialise, to the degree that would like to see, at least. In the 1970s and 1980s Saudi Arabia could push western economies into recession by restricting its oil production and ramping up the price of a barrel of crude. With more energy-efficient economies, the shale gas revolution, and a weakening of Opec that is no longer such a potent threat.

The Khashoggi affair brings Saudi Arabia further scrutiny about its wider conduct, not least the merciless war in Yemen. Some 13 million people in Yemen are facing starvation in the worst famine for 100 years. Much of this approaching fresh humanitarian disaster can be attributed to the unflinching way Saudi Arabia and its allies have prosecuted their war, in effect a proxy conflict between the kingdom and Iran. So far, at least 10,000 people have been killed in the conflict and millions are displaced in this dirt-poor land.

Riyadh must sense by now that the west is so concerned about its policies towards internal dissent and external threats that the diplomatic and military support that America and Europe have hitherto supplied can no longer be taken for granted. There are also concerns about the treatment of Shia minorities in the east of Saudi Arabia, and interference further afield – as there is with the other regional superpowers, Israel, Turkey and, most dangerously, Iran. According to Amnesty International, “torture and other ill-treatment of detainees remained common and widespread. Courts continued to convict people and uphold death sentences on the basis of contested pre-trial ‘confessions’. Security officials continued to torture and otherwise ill-treat detainees with complete impunity.” This is not the foundation of a secure state.

It is in nobody’s interests to see an unstable Saudi Arabia. The kingdom has enemies enough, at home and abroad, without making matters far worse for itself through counterproductive policies such as the war in Yemen and the lack of transparency in the Khashoggi affair. Now is a moment for its reforming crown prince to bring about some more fundamental changes and greater openness than he has delivered so far.