In recent years Vladimir Putin, Russia’s president, has been an unconstructive actor on the world stage, notorious for his protection of the murderous Assad regime in Syria and for the annexation of Crimea. But how he acts following the shooting down of a Malaysian airliner over Ukraine will probably do more than anything else to seal his international reputation.

It may be that this terrible tragedy, in which 298 innocent people died, will convince the Kremlin leader to shut down the bloody insurgency in eastern Ukraine that he has fuelled by covertly supplying arms to the pro-Russian rebels fighting the Kiev government. Alternatively, he may try to prevent the truth over Malaysia Airlines Flight 17 emerging and stick to his policy of dismembering Ukraine to stop it shifting to the west. If he chooses the latter course, Russia will become an international pariah and a dark new era in east-west relations will begin.

Following the destruction of MH17, there has been much dispute as to who was responsible. The circumstantial evidence indicates that the aircraft was shot down by pro-Russian separatists. There is a question mark over how the rebels came to be in possession of such a potent surface-to-air missile system. They may have stolen it from the Ukrainian military or – far more gravely – obtained it directly from Russia. But it seems inconceivable that the Boeing 777 was fired on by Ukraine’s armed forces, given the absence of any military aircraft on the rebel side.