While the Assad regime in Damascus has denied responsibility for the sarin gas missiles that killed around 1,400 Syrians in the suburb of Ghouta on 21 August, information is now circulating in the city that Russia's new "evidence" about the attack includes the dates of export of the specific rockets used and – more importantly – the countries to which they were originally sold. They were apparently manufactured in the Soviet Union in 1967 and sold by Moscow to three Arab countries, Yemen, Egypt and Colonel Muammar Gaddafi's Libya. These details cannot be verified in documents, and Vladimir Putin has not revealed the reasons why he told Barack Obama that he knows Assad's army did not fire the sarin missiles; but if the information is correct – and it is believed to have come from Moscow – Russia did not sell this particular batch of chemical munitions to Syria.

Since Gaddafi's fall in 2011, vast quantities of his abandoned Soviet-made arms have fallen into the hands of rebel groups and al-Qa'ida-affiliated insurgents. Many were later found in Mali, some in Algeria and a vast amount in Sinai. The Syrians have long claimed that a substantial amount of Soviet-made weaponry has made its way from Libya into the hands of rebels in the country's civil war with the help of Qatar – which supported the Libyan rebels against Gaddafi and now pays for arms shipments to Syrian insurgents.

There is no doubt that Syria has a substantial chemical weapons armoury. Nor that Syrian stockpiles contain large amounts of sarin gas 122mm missiles. But if the Russians have indeed been able to identify the specific missile markings on fragments found in Ghouta – and if these are from munitions never exported to Syria – the Assad regime will boast its innocence has been proven.

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In a country – indeed a world – where propaganda is more influential than truth, discovering the origin of the chemicals that suffocated so many Syrians a month ago is an investigation fraught with journalistic perils. Reporters sending dispatches from rebel-held parts of Syria are accused by the Assad regime of consorting with terrorists. Journalists reporting from the government side of Syria's front lines are regularly accused of mouthing the regime's propaganda. And even if the Assad regime was not responsible for the 21 August attacks, its forces have committed war crimes aplenty over the past two years. Torture, massacre, the bombardment of civilian targets have long been proved.

Nevertheless, it also has to be said that grave doubts are being expressed by the UN and other international organisations in Damascus that the sarin gas missiles were fired by Assad's army. While these international employees cannot be identified, some of them were in Damascus on 21 August and asked a series of questions to which no one has yet supplied an answer. Why, for example, would Syria wait until the UN inspectors were ensconced in Damascus on 18 August before using sarin gas little more than two days later – and only four miles from the hotel in which the UN had just checked in? Having thus presented the UN with evidence of the use of sarin – which the inspectors quickly acquired at the scene – the Assad regime, if guilty, would surely have realised that a military attack would be staged by Western nations.

As it is, Syria is now due to lose its entire strategic long-term chemical defences against a nuclear-armed Israel – because, if Western leaders are to be believed, it wanted to fire just seven missiles almost a half century old at a rebel suburb in which only 300 of the 1,400 victims (if the rebels themselves are to be believed) were fighters. As one Western NGO put it yesterday: "if Assad really wanted to use sarin gas, why for God's sake, did he wait for two years and then when the UN was actually on the ground to investigate?"

The Russians, of course, have made similar denials of Assad's responsibility for sarin attacks before. When at least 26 Syrians died of sarin poisoning in Khan al-Assal on 19 March – one of the reasons why the UN inspectors were dispatched to Syria last month – Moscow again accused the rebels of responsibility. The Russians later presented the UN with a 100-page report containing its "evidence". Like Putin's evidence about the 21 August attacks, however, it has not been revealed.

A witness who was with Syrian troops of the army's 4th Division on 21 August – a former Special Forces officer considered a reliable source – said he saw no evidence of gas shells being fired, even though he was in one of the suburbs, Moadamiya, which was a target for sarin. He does recall the soldiers expressing concern when they saw the first YouTube images of suffocating civilians – not out of sympathy, but because they feared they would have to fight amid clouds of poison.

"It would perhaps be going beyond conspiracy theories to say the government was not involved," one Syrian journalist said last week, "but we are sure the rebels have got sarin. They would need foreigners to teach them how to fire it. Or is there a 'third force' which we don't know about? If the West needed an excuse to attack Syria, they got it right on time, in the right place, and in front of the UN inspectors."