It is now beyond dispute that banned chemicals have been used in the Syrian conflict. Aside from a few conspiracy theorists, all sides – including the Russian and Syrian governments – accept this as fact, though they disagree about who is responsible.

We have reached this point because of painstaking work by the Organisation for the Prohibition of Chemical Weapons over the last four years in gathering evidence. The OPCW's Fact Finding Mission is continuing its investigations in Syria but during the next few months a joint UN/OPCW team will also be working "to identify, to the greatest extent feasible, perpetrators who use chemicals as weapons in the Syrian Arab Republic".

This team, known in UN-speak as the Joint Investigative Mechanism (or JIM for short), has a three-person leadership panel headed by Edmond Mulet from Guatemala. He is assisted by Malaysian-born Judy Cheng-Hopkins and Stefan Mogl from Switzerland. The panel hopes to report back in mid-October.

Investigator Edmond Mulet: working "to identify, to the greatest extent feasible, perpetrators who use chemicals as weapons in the Syrian Arab Republic"

Initially, the JIM will focus on two specific incidents. One is the Sarin attack in Khan Sheikoun on 4 April which, according to reports at the time, killed at least 74 people and injured hundreds more. The other is a mustard gas attack in Um Housh, in Idlib province, last September which injured two women.

However, these may not be the only ones. At a press conference yesterday, Mulet said the OPCW is currently working on "six or seven other cases that might come our way before the end of October".

The focus on Um Housh in addition to Khan Skeihoun appears to be a compromise in order to secure Russian agreement for the JIM investigation to go ahead. Although Um Housh was far less serious in terms of casualties it nevertheless involved a banned weapon and Russians have been eager to highlight it – presumably because (unlike the Khan Sheikhoun attack) locals blamed ISIS.

One criticism of the recent OPCW report on Khan Sheikhoun is that the Fact Finding Mission did not visit the town or Shayrat airbase from where the attack is thought to have been launched. Following the use of Sarin in Khan Sheikhoun, Donald Trump ordered strikes on Shayrat with 59 Tomahawk cruise missiles at an estimated cost of $49 million.

At yesterday's press conference, Mulet said: "It is our intention to visit al-Shayrat base in order to go to the site, and we also would like to go to Khan Sheikhoun. But of course that is related to security concerns and security issues."

The pros and cons of visiting both these places were discussed by Aron Lund of the Century Foundation in an article published on 30 June. As the recent OPCW report noted, it is questionable whether much useful information can be gathered in Khan Sheikhoun so long after the event. The need for an inspection visit to Khan Sheikhoun has been further reduced by the OPCW's revelation in its report that the Syrian government provided samples said to have been collected in the town which tested positive for Sarin.

At the press conference, Mulet appeared to suggest that visits to Khan Sheikhoun and Shayrat would be conditional on the Syrian government cooperating over related matters. He said:

"Before we are going to these places I would need some feedback from the Syrian government. I need information about the flight logs in al-Shayrat, the movements around al-Shayrat. I need the names of the people we will be interviewing – military commanders and government officials – and also some information that the Syrian government could provide to us in order to conduct our work. So, we are working already with the Syrian government on this, and hopefully we will be given the necessary tools and instruments in order to our work."

As a party to the Chemical Weapons Convention, Syria has an obligation to cooperate. How far it will do so, though, is still an open question. This raises the possibility of cat-and-mouse antics similar to those with UN weapons inspectors in Iraq which led, eventually, to the US-led invasion of 2003.

It is important to avoid that. Clearly, there are some who would like to make chemical weapons an excuse for deeper military involvement in Syria but I have argued several times before (here and here) that the chemical issue should be kept as separate as possible from the wider confict.

The banning of chemical weapons has been a great example of international cooperation and so far only three countries – Egypt, North Korea and South Sudan – have neither signed nor ratified the convention. Failure to confront the use of chemical weapons in Syria would blow a huge hole in what has been achieved so far and signal to others that they can use them with impunity.

But cruise missiles won't help. What it needs is a careful, patient, evidence-based and sustained effort by the UN to bring those responsible for poisoning people in Syria to justice – no matter how long it takes.