The Joint Investigative Mechanism (JIM) was set up last year by the UN Security Council in response to reports of nine reported cases of the use of chemical weapons.
The panel was able to identify who was responsible for three of these nine cases.
It says that President Bashar al-Assad's regime dropped chemical weapons on two villages in north-western Idlib province: Talmenes on 321 April 2014 and Sarmin on 16 March 2015.
The panel also found that IS most probably used sulphur mustard, better known as mustard gas, in an attack on the town of Marea in northern Aleppo province on 21 August 2015.
“I want to make it absolutely clear to Assad and those under his command: the world is watching,” said US President Barak Obama when the use of chemical weapons was first reported in 2013.
“The use of chemical weapons is and would be totally unacceptable. If you make the tragic mistake of using these weapons there will be consequences and you will be held accountable.”
They are looking for some acceptance from the Russians that Assad is at fault and therefore maybe some progress on re-introducing a significant cease-fire.
Assad's government declared that it would fully cooperate with the inquiry that was put under the auspices of the The Hague based Organisation for the Prohibition of Chemical Weapons [OPCW].
“The main part of this agreement is to not to manufacture these armaments, not to store and not to use. And of course not to distribute. And part of it is to get rid of those chemical materials, to destroy them,” said Assad when signing the OPCW agreement aimed at clearing existing stockpiles.
But, in spite of investigations and months of collecting, shipping and destroying stockpiles of Syria’s chemical weapons, there were still violations.
The first attacks used sarin gas but, once that had been eliminated by the UN programme, attacks took place using chlorine, says Dzenan Sahovic, director of CBRNE Centre that helps train weapons inspectors.
“You can interpret it in many ways, either they gave up all the sarin and are now using chlorine. And then the other interesting thing is that there is good evidence that mustard gas was used not by the regime but by the rebel forces.”
But JIM goes beyond establishing whether chemical weapons were used. Its mandate is to establish who pulled the trigger.
“The very specific task of the JIM, which is a joint investigative mission linking the UN with the Organisation for the Prohibition of Chemical Weapon,s is to identify the people or parties responsible for the use of chemical weapons in Syria,” says Rosemary Hollis, a professor of Middle East Studies at City University London.
“The JIM carries with it in implication that, having reported back to the UN which it is currently in the process of doing on who is responsible for the use of chemical weapons, it implies action by the UN.”
In the case of IS, this may be easy as all parties oppose them. But punishing Damascus may prove more complicated.
“There is an understanding on the part of the French, British and Americans on the UN Security Council,” says Hollis, “that they cannot expect the Russians or indeed the Chinese to abandon the Assad government completely and support punitive actions against the Assad government which stands accused by the JIM of the use of chemical weapons.
"In those circumstances, I get the sense from French statements that they are looking for some contrition from the Russians, some acceptance that Assad is at fault and therefore there may be some progress on reintroducing a significant ceasefire to the hostilities currently being pursued by the Assad regime in Syria."
The UN Security council will talk about this report next week and decide what action to take.