IN AN interview Tuesday with the Associated Press and Russian television, Russian President Vladimir Putin threw a bucket of cold water on the assertions of the United States and others that Syrian troops used chemical weapons in the Aug. 21 attack that killed 1,429 people near Damascus. “If there is evidence that chemical weapons have been used, and used specifically by the regular army, this evidence should be submitted to the U.N. Security Council,” he said. “And it ought to be convincing. It shouldn’t be based on some rumors and information obtained by intelligence agencies through some kind of eavesdropping, some conversations and things like that.”

“Ludicrous,” Mr. Putin said of the possibility that Syrian troops carried out the attack. In another interview, he called it “utter nonsense.” Mr. Putin has been a stalwart backer of Syrian President Bashar al-Assad in the civil war, but that does not give him license to ignore the facts and gloss over inconvenient truths. Syria’s chemical weapons stockpile had its origins in Cold War deals with the Soviet Union, a patron of the Syrian army, including transfers of aerial bombs that could be filled with sarin and Scud missiles armed with warheads that could carry agents such as VX nerve gas.

If Mr. Putin doubts whether chemical weapons were used by the Syrian army, perhaps he could ask his former colleagues at the Federal Security Service to dig into their archives and those of the Soviet KGB, where Mr. Putin also served. He might want to see the dossier on retired Lt. Gen. Anatoly Kuntsevich, who in the last decade of the Cold War directed a secret Soviet chemical weapons testing facility.

Gen. Kuntsevich was awarded the Lenin Prize for his work on a new binary chemical weapon. In early 1992, after the Soviet collapse, Russian President Boris Yeltsin named him to head a commission to oversee the demilitarization of chemical and biological weapons. But only two years later, Mr. Yeltsin fired him for “one-time gross violation of work responsibilities.” Russian officials later disclosed that Gen. Kuntsevich was investigated for helping arrange a delivery of about 1,700 pounds of nerve-gas precursor agents to Syria. He was never prosecuted in Russia, but in November 1995, the United States imposed sanctions on Gen. Kuntsevich for “knowingly and materially assisting” Syria’s chemical weapons program. The general died in 2002 on a flight from Syria to Russia.

Mr. Putin cannot be held to account for every military contract of the Soviet Union nor for the dirty deals of a rogue general in the 1990s. Over the past two decades, Russia has cooperated with the United States in destroying chemical weapons stockpiles. But the sarin gas attack near Damascus should not be so glibly dismissed as “ludicrous” by a Russian president. Instead of mocking the West, Mr. Putin should throw Russia’s support behind an investigation of this atrocity. A horrible crime was committed on a killing wind in Syria, and given Russia’s past, Mr. Putin cannot simply look the other way.