RUSSIA HAS destroyed all of its Cold War chemical weapons stocks, President Vladi­mir Putin boasted Oct. 19 when he appeared before the Valdai forum in Sochi. He said Russia had "made a significant contribution to enhancing international security" by liquidating the bombs and artillery shells, "enough to destroy life on the planet many times over," and he chided the United States for falling behind in this important work.

Five days later, the U.N. Security Council prepared to vote to extend for one year the mandate of the investigation into the use of nerve gas in Syria. That inquiry includes the April 4 attack on Khan Sheikhoun , an opposition-held village in Syria, where nerve agents killed at least 87 people. The United States, Britain and France have accused the forces of Syrian President Bashar al-Assad of carrying out the attack, in which deadly sarin was dispersed.

And what of Russia's abhorrence of chemical weapons? Not so much in Syria, apparently. Russia, a permanent member of the Security Council, on Tuesday vetoed the extension, standing up for Mr. Assad's brutal killing machine rather than the lofty principles advertised at Valdai. In fact, Russia and the United States had earlier backed the probe in Syria, known as the Joint Investigative Mechanism (JIM), to finger those responsible for chemical attacks in Syria's six-year war. The mandate for the probe expires Nov. 17, and it should be renewed. A JIM panel declared Thursday after an investigation that it is "confident that the Syrian Arab Republic is responsible for the release of sarin" at Khan Sheikhoun.

Russian officials said they wanted to see the report before deciding whether to extend the investigation. Now it is out and time to act. There is more to investigate and document about the use of these horrible weapons.

If the international investigation in Syria stalls because of the Russian veto, it is possible that no one will be held to account for the Khan Sheikhoun atrocity. Mr. Putin often expresses a desire for Russia's views to be treated with respect, but what kind of respect is due if he favors a besieged dictator who is using chemical weapons?

Russia deserves credit for destroying its Cold War chemical weapons stocks. In just one compound in southern Russia near the town of Shchuchye, the Soviet Union left behind about 1.9 million projectiles filled with 5,460 metric tons of sarin and other nerve agents. These were liquidated, safely, in a mammoth factory. Mr. Putin bragged at Valdai that "we found the money to build plants for the destruction of chemical weapons." What he didn't mention is that the United States gave Russia $1 billion to carry out the destruction at Shchuchye alone.

Mr. Putin forgets such inconvenient truths. Now comes a choice: to hide another such inconvenient truth and shield those who continue to use chemical weapons; or really to stand up for their elimination.