Does Syria’s Bashar al-Assad still have chemical weapons, and why would he use them?

The reliability of sources in the Syrian civil war is always in question - particularly when verifying pictures and video shared on social media is involved.

We know for a fact that on 4 April, 87 people in the village of Khan Sheikhoun died after exposure to what extensive testing by the Organisation for the Prohibition of Chemical Weapons (OPCW) said was sarin or a chemically similar banned toxin.

What we lack is a definitive answer as to who is responsible for their deaths. President Bashar al-Assad and Syria’s rebels as usual blamed each other, pointing out it is not in their strategic interests to gas scores of civilians.

Both the far-left and far-right settled on conspiracy theories claiming the opposition either faked the attack or used sarin on their own people in order to manufacture worldwide outrage at the Syrian regime. Damascus and Moscow, on the other hand, said that the casualties occurred when a conventional air strike hit an al-Qaeda-affiliated weapons depot, releasing the deadly gases in the explosion.

Yet the overwhelming evidence - gathered from radar and satellite imagery, eyewitness reports, medical charities, Western intelligence services and geolocated photos and video - supports the conclusion that the Syrian government deliberately used sarin in Khan Sheikhoun.

1. Does the Syrian government still have chemical weapons?

   It seems likely.

   There have been sporadic reports of chemical weapons use since the war broke out in 2011. In 2013 the regime agreed to surrender its chemical arsenal to the Organisation for the Prevention of Chemical Weapons (OPCW), an international watchdog, as a mark of transparency.

   Since then, however, war monitors such as the UK-based Syrian Observatory for Human Rights report there have been dozens of alleged chemical attacks.

   While blame has not been assigned in the majority of cases, a joint report from the UN and the OPCW found Mr Assad’s forces explicitly responsible for chlorine attacks on Talmenes in April 2014 and Sarmin in March 2015, both of which the government has denied involvement in.

   Since the Khan Sheikhoun attack, the US, Israel, and France have all said intelligence reviews suggest the regime does still have chemical weapons at its disposal.

2. Why don’t we know if the regime gave them all up?

   The Syrian government is insistent it has, although the opposition has long accused it of not declaring its entire stock, and of continuing to manufacture agents on a small scale.

   During OPCW investigations, 21 weapon-making sites were confirmed to have dismantled or destroyed their equipment, while a further two were believed to have been abandoned.

   Officials from the Obama administration said they always believed it was possible some weapons had been held back, trying to refer instead to the destruction of Syria’s “declared” chemical weapons stocks, although the nuance was often lost.

   While the UN has called for an immediate international investigation into the latest attack, a proposed resolution was vetoed by permanent Security Council member Russia.

   Mr Assad will not allow any investigation into the Khan Sheikhoun incident unless it is “impartial” and not used “for politicised purposes,” he said in an interview a week after the attack.

3. Could anyone else have carried out the Khan Sheikhoun attack?

   In a nutshell, no.

   Neither side disputes the fact there was an air strike. The issue is where it hit, and which weapons were involved.

   Eye witnesses and medical workers present in the 4 April incident have said the strike occurred at around 6.30am. They say they initially didn’t realise the attack involved chemical agents rather than conventional munitions.

   Damascus and its allies in Moscow have said the casualties were caused by gases released after an al-Qaeda-affiliated ammunitions depot was hit by conventional munitions in a legitimate government air raid - although they have not produced any evidence for this claim.

   Syria and Russia have often accused rebels of possessing chemical weapon caches and equipment smuggled in from Libya. Even if that were the case, geolocation of pictures and video from the village shows the impact blast from the suspected sarin bomb hitting the middle of a residential street dozens of metres away from the alleged weapons depot.

   Bellingcat notes that because of the way most sarin components are stored, even a direct hit on a warehouse could not create the large quantities of deadly sarin released in the attack.

   The Russian and Syrian accounts also don't add up timewise. The Russian Foreign Ministry claimed the attack on the weapons warehouse took place at around 8.30am - two hours later than all other evidence suggests. Mr Assad said the attack took place at around 11am.

   While Isis has created its own rudimentary mustard gas, in some cases using it on civilians in both Syria and Iraq, it does not possess anything as powerful as the agents used in Khan Sheikhoun, nor does it have an air force.

4. Why would the Syrian government use chemical weapons if it’s winning the war?

   It can be argued provoking international outrage by using an indiscriminate and particularly lethal weapon such as sarin on civilians was not in the Syrian government’s interests - especially considering it militarily now has the upper hand in the war.

   The best answer is that since the US did not take direct action in 2013 after the Ghouta sarin attack which killed hundreds, the Syrian government may have been led to believe it could use chemical agents without fearing any consequences.

   Russia has also shielded Syria from criticism over chemical weapons use in the past, to the point of accusations from investigators of obfuscating evidence.

   Such attacks are effective at striking horror into the opposition. While the regime no longer has to make concessions to weakened rebel forces, the war is far from over; dropping atomic bombs on Japan hastened World War II to a quicker conclusion.

   US President Donald Trump had previously made it clear his policy in Syria would be defeating Isis rather than removing Mr Assad from power. The week before the attack, White House Press Secretary Sean Spicer said that the Syrian president's seat at the table was a “political reality.”

   Once again, it appears the penalty for using chemical weapons may be minimal.

   While the "warning shot" retaliatory launch of 59 Tomahawk missiles at a Syrian airbase near Homs may make the Assad government reconsider their use in future, its usual ‘scorched earth’ conventional bombing campaigns over rebel-held areas quickly resumed.