In death he is achieving his life’s work. Jamal Khashoggi was a Saudi patriot and reformer, whose journalism helped expose the reality of Saudi Arabia and the cosseted, hypocritical relationship the kingdom enjoys with the west. Through his brutal, pitiless death, he has succeeded more effectively in that mission than he could ever have imagined.

The brightest light shone by the dissident journalist through his murder is, of course, on the morally repugnant nature of the regime that rules the nation he fled. The nauseating details of his killing, according to Turkish leaks – the bone saw; the instruction from the lead limb-chopper, a doctor, to his colleagues to put on headphones and listen to music to distract themselves from the gruesomeness of their task; the hasty repaint of the walls of the Istanbul consulate – confirm what we already knew. The House of Saud is itself soaked in blood.

It’s the very least we can do – to force the world to look into the darkness of the desert kingdom

Besides its record of beheadings and amputations at home, Saudi Arabia has spent three years creating carnage in Yemen, and starving one of the world’s poorest nations of food and medicine – thereby imposing a crisis long deemed by the UN to be the planet’s worst humanitarian disaster. I can understand the frustration of campaigners for Yemen that the death of one man has captured a global attention that has so rarely focused on the tens of thousands killed in that dirtiest of wars. But sometimes it takes the story of a single individual – his life and death – to break through. So it has proved with Khashoggi.

His death has illuminated not only a general truth about Saudi Arabia, but the specific ugliness of its current ruler, Crown Prince Mohammed bin Salman. Analysts say that, from the start, Bin Salman has been in the business of demonstrating power. The war on Yemen, of which he is credited as the architect, has been about projecting Saudi strength, as was last year’s arrest and imprisonment of hundreds of potential challengers to his authority, including members of his own family. The sheer brazenness of Khashoggi’s murder in a foreign country – with 15 Saudi officials flying into Istanbul carrying equipment to dismember a body, later followed by a squad of cleaners bearing mops before the Turkish authorities could inspect the premises – suggests a ruler who wanted to send a message: I can kill my enemies with impunity.

And who can blame him for thinking that? After all, the world has barely acted to stay his hand in Yemen, or even to pay it much attention. A similar shrug greeted the Saudi abduction of Saad Hariri, Lebanon’s prime minister, during a visit to Riyadh last November – when, in the manner of a hostage video, Hariri was forced to read out a resignation statement that his Saudi hosts/captors had written for him.

Play Video 1:01 Trump denies ‘giving cover’ to Saudis in Khashoggi case – video

This, then, is the style of a young autocrat who only recently established a “tiger team” to conduct covert special operations, which sounds a lot like a death squad charged with hunting down anyone unlucky enough to find themselves on Bin Salman’s enemies list.

It seems Bin Salman has now picked an intelligence official as his fall guy for the Istanbul murder, but his earlier lines of defence are instructive. For a while, state-controlled media were claiming that the 15 Saudi heavies caught on Turkish CCTV were in fact “tourists” unfairly accused. One wonders if they were drawn to St George’s Cathedral in Istanbul perhaps by its unusually tall spire.

Of course, such excuses are all but meant to be laughable, to advertise the killers’ impunity – just as they were when they were offered by the alleged poisoners of the Skripals, who insisted they were in Salisbury to see the sights. Which brings us to yet another truth confirmed by Khashoggi in death: western hypocrisy. Those in Washington or London who, rightly, demanded Moscow face swift punishment for the attempted murder of the Skripals found themselves tongue-tied when it came to acting against Riyadh. Suddenly they needed to wait for a full investigation, albeit one conducted by the Saudis themselves. Imagine how they would have, rightly, mocked the notion of an inquiry conducted by Chief Inspector Putin.

This double standard is not confined to governments, incidentally. Among those who, rightly, condemn the hypocrisy of the west, and who demanded instant action against Saudi Arabia, were some who were oddly more cautious in the Skripal case, open to all kinds of alternative, even wild explanations. In the same way, some of those who are, rightly, outraged by the slaughter in Yemen are curiously slow to show anger about the bloodshed in Syria. And yet a life taken is a life, whether it’s taken by a western ally, like Saudi Arabia or Israel or the US itself, or by a western enemy, such as President Assad or Putin.

Of course, there’s nothing new about double standards and Saudi Arabia: British and US governments have been compromised for decades, thanks to dependence on Saudi oil and arms sales. Yet Khashoggi has put up in lights what is novel about the Trump era. For one thing, Trump is more open than his predecessors, admitting out loud that he doesn’t want to risk lucrative weapons deals.

Evidence suggests crown prince ordered Khashoggi killing, says ex-MI6 chief Read more

But he is also personally compromised, thanks to business ties – especially involving his son-in-law Jared Kushner – that point to a possible financial dependence on Bin Salman. What’s more, while previous US presidents at least paid lip service to Saudi human rights violations, Trump has cheered Bin Salman’s every move towards autocracy. (“Strongman” is Trump’s favoured form of government.) Note how in the very week that Saudi Arabia stands accused of murdering a journalist, Trump applauded a US politician for having body-slammed a reporter (my Guardian colleague, Ben Jacobs). Again, who can blame Bin Salman if he believed Trump would indulge his version of robust action to curb a troublesome press?

Kushner reportedly reckons that Bin Salman can ride out this current storm, that the media will soon lose interest. Others will hope that the realpolitik argument will prevail: that the west can’t act against the Saudis because we need them too much. But that’s nonsense. Riyadh does not cooperate with the west against terrorism or Iran for altruistic reasons: it does so out of self-interest. That self-interest will remain, even if Britain, the US and others move now to impose Magnitsky-style sanctions on those responsible for this outrageous murder. It’s the very least we can do, if only to honour a man who in death achieved what he sought to do in life – to force the world to look into the darkness of the desert kingdom.

• Jonathan Freedland is a Guardian columnist