It is now more than a month since the murder of the Saudi journalist Jamal Khashoggi — and I am starting to have an appalling suspicion.

I don’t have any doubt about what happened: the plot to lure him to the Saudi consulate; the savage attack by heavies from Crown Prince Mohammed bin Salman’s own security team; the dismembering of the body.

Nor do I doubt for a second that this disgusting assassination was ordered at the highest levels of the Saudi regime.

But it is not the forensics that bother me. There is another reason for my nagging anxiety.

After more than a month, we still have no body, and no credible account of how and when an explanation might be forthcoming.

We have no clear understanding of how it is proposed that those responsible for this atrocity will be brought to justice, or in what forum this might take place.

For all the talk of sanctions for the guilty, it is far from clear how they will be identified, or where they will be tried.

It is all too easy to see how Khashoggi’s case could end up in a murky netherworld in which the straightforward requirements of criminal justice may be warped by the expedients of geopolitics and diplomacy.

My awful suspicion, and I pray I am wrong, is that for one reason or another, the killers, or at least those who ultimately gave the order, may get away with it.

There are simply too many powerful people who would frankly prefer that the whole business be brushed under the carpet.

There are too many people who look at the state of the Middle East — and think that we simply can’t afford to take this investigation to its logical conclusion.

They look at the pivotal role of Saudi Arabia, and they think about what might happen if that government were seriously destabilised — and they shudder.

Israeli Prime Minister Benjamin Netanyahu spoke for this school of thought when he said that of course the killers of Jamal Khashoggi should be brought to justice — but the real problem was Iran.

And Netanyahu is certainly right that Iran is a serious problem.

The government in Tehran remains a disruptive force, bent on expanding its role in the region. We see excessive Iranian influence in Lebanon, in Iraq, in Syria and in Yemen.

That influence needs to be diminished. But we will not put Iran back in its box unless we accept that the Iranians are also highly skilful at exploiting the consequences of the policies of the West and its allies.

In Lebanon, the Iranians made the most of resentments that followed the Israeli invasion of 1982.

In Iraq, they found the whole country was virtually handed to them on a plate after the removal of the Sunni regime of Saddam Hussein in 2003.

In Syria, they poured into the gap left by the West’s limp-wristed and ultimately abortive attempts to remove Bashar al-Assad.

And as for Yemen — the Iranians had virtually no influence in Yemen at all, and no real strategic interest, until the Saudi-led coalition began its ill-fated campaign of aerial bombardments against the Houthi rebels.

Let us be in no doubt: There is a sense in which the Saudis and their allies are in the right. The Yemeni government was illegally overturned.

The actions of the coalition are supported by a UN resolution. But the plain fact is that the campaign has not been successful.

In the three years since the Saudis launched their offensive, Yemen has been brought to the brink of starvation — and the Houthis have been driven so far into the arms of Iran that in the past year they have actually started firing Iranian-built missiles at Saudi Arabia.

This war needs to come to an end — and it can.

The excellent UN special envoy to Yemen, Martin Griffiths, is proposing a deal that would bring an end to the conflict, give the Houthis some say in the government of Yemen, and ensure that Iran is constitutionally precluded from having a role in the country.

That is why it was right that last week both Defense Secretary Jim Mattis and Secretary of State Mike Pompeo decided to increase the pressure on Saudi Arabia. We need a ceasefire.

And at this critical moment, it is vital that the long-term strategic partners of Saudi Arabia, both Britain and the United States, are frank in the way that friends are entitled to be frank.

The war in Yemen is turning out to be bad for Saudi Arabia and, alas, is boosting, not reversing, Iranian influence.

The murder of Khashoggi has been terrible for Saudi Arabia — and if there is one way to boost Iran, and all regional critics of the Saudi regime, it would be to hush it all up. Jamal Khashoggi’s killers must be found, and justice done, though the heavens fall.

• Boris Johnson is the former British foreign secretary and Mayor of London