The slaying of the journalist Jamal Khashoggi was a barbaric act, ordered and carried out by barbarians. It cried out for justice – which means, inevitably, a trial. Yet all the British government is demanding is an “investigation” – by the same Saudi state that spent 17 days lying about its responsibility and is still offering unbelievable excuses for the murder. Any Saudi investigation would, at most, offer up a few scapegoats who would be subjected to a secretive procedure and in reality punished for their incompetence rather than their guilt.

But this was an international crime that took place in breach of United Nations conventions in the precincts of a consulate enjoying inviolability under international law. It involved the silencing of a US-based journalist for exercising the right of freedom of speech – a right also belonging to all his potential readers, and guaranteed under every international human rights convention. It was an action by a UN member state that threatens peace and security and it should be taken up by the UN security council, which has acted before to set up tribunals to deal with similar atrocities – the assassination of the Lebanese prime minister Rafik Hariri, for example, and the Lockerbie bombing.

President Erdoğan has called for a trial of the suspects – most obviously, the 15-strong hit squad – to take place in Turkey. That would be reasonable were it not for the fact that Erdoğan himself has emasculated Turkey’s legal system by sacking so many judges, imprisoning lawyers and using the courts to persecute his own journalist critics. Moreover, any trial in Turkey would run into evidential problems resulting from the inviolability of the consulate, an issue that need not trouble an international court set up by the security council. And even if Saudi Arabia were prepared to extradite a few of the killers to Turkey, they would be schooled and rehearsed and forbidden (even if they knew) from identifying the men who gave the orders.

There are enough precedents for the security council, under its chapter VII power, to act so as to avoid international conflict, to set up a court to research and punish the carefully planned assassination of a journalist in a member state by agents of another member state. There are plenty of experienced judges available who have dealt with atrocities in the Balkans, Rwanda and Sierra Leone, and prosecutors well qualified for mounting cases of international crimes. The Turkish authorities have ample evidence against the immediate perpetrators and western and Israeli intelligence agencies can undoubtedly supplement what is already known about the Saudi chain of command.

Jamal Khashoggi: murder in the consulate Read more

Continuing pressure from the security council and orders by the court, backed by sanctions against powerful Saudis (preventing them from travelling to Europe or using schools and health services), trade boycotts and sanctions, and threats of diplomatic isolation, could force the Saudi crown prince, Mohammed bin Salman, to send suspects to The Hague, as it forced Gaddafi to cooperate over Lockerbie, and to disclose evidence that, when analysed together with other evidence, might lead a chief prosecutor to include him in the charge sheet – at least as an “unindicted co-conspirator”. Only an international legal process can establish with any credibility whether Bin Salman actually gave the lethal order, or perhaps said in the manner of King Henry II: “Will no one rid me of this troublesome priest?”

Realpolitik – as Jeremy Hunt has hinted and Donald Trump has megaphoned – dictates that Saudi Arabia is too important to be pushed too far because of its oil wealth, its arms purchases and its intelligence about terrorists. The most disgraceful moment for British justice came when our highest court yielded to demands from the Blair government to drop the bribery case against BAE and its high ranking Saudi recipients. The crown prince himself may be too big to jail, but the only prospect of getting at the truth about this hideous event will come from the establishment of an international court.

• Geoffrey Robertson QC is author of Crimes Against Humanity: The Struggle for Global Justice