Based on the following tweet it looks like today’s OPCW IIT report will be focused on Sarin and chlorine attacks in Al-Lataminah (not the Douma attack), so in this thread we’ll look at what we already know https://twitter.com/CanadaOPCW/status/1247512834512162816

The OPCW IIT is currently investigating 9 attacks. The Al Lataminah attacks occurred on March 24th, 25th, and 30th 2017, with the March 24th and 30th attacks being Sarin, and chlorine on March 25th.

During March 2017, and throughout 2017, Al-Lataminah and other towns in the Idlib region were reportedly targeted by multiple chemical attacks. @GPPi’s new searchable chemical weapon attack dataset details those reports.
https://chemicalweapons.gppi.net/data-portal/ 

Unlike the Khan Sheikhoun Sarin attack on April 4th 2017 very little, if any attention, was paid to the Al-Lataminah attacks, with minimal mainstream media coverage, and as a result they went largely unnoticed until later in the year.

The March 30th 2017 attack was referenced in the August 2017 Report of the Independent International Commission of Inquiry on the Syrian Arab Republic, which provided details of the attack and Sarin like symptoms, but didn’t specify Sarin was used
https://ap.ohchr.org/documents/dpage_e.aspx?si=A/HRC/36/55

It wasn’t until October 2017 that OPCW head Ahmet Uzumcu stated Sarin was used in the March 30th 2017 Al-Lataminah attack, after which Bellingcat began to investigate the incident
https://www.dw.com/en/sarin-gas-was-used-in-another-syria-attack-this-year-chemical-weapons-watchdog-says/a-40809222

Our investigation discovered few references to the March 30th attack. A rare media report on the incident March 30th attack was Reuters March 30th article, which also referenced the March 25th chlorine attack currently being investigated by the OPCW-IIT
https://www.reuters.com/article/us-mideast-crisis-syria-hama/warplanes-strike-near-syrias-hama-as-army-counter-attacks-idUSKBN1711O9

We also discovered a March 31st Facebook post by the Hama Health Directorate that provided details of the March 30th attack, which detailed victims in a number of attacks, including victims of a chemical attack on March 30th
https://www.facebook.com/HamaHealthDirectorate/photos/a.480726425390198.1073741828.473950772734430/1167244963405004/?type=3&theater

In @hrw's May 2017 report, Death by Chemicals, Anwar Rahmoun, a local farmer, described details of the attack, providing details consistent with other eyewitness accounts of the attack
https://www.hrw.org/report/2017/05/01/death-chemicals/syrian-governments-widespread-and-systematic-use-chemical-weapons#88df05

According to the @hrw report, the Syrian American Medical Society stated that 169 individuals were treated for chemical exposure, with no fatalities recorded
https://www.hrw.org/report/2017/05/01/death-chemicals/syrian-governments-widespread-and-systematic-use-chemical-weapons#88df05

A statement by @UOSSM stated at least 70 civilians were injured from exposure to a chemical agent, detailing symptoms consistent with Sarin exposure, and included an image of the constricted pupil of one victim, consistent with Sarin exposure
https://myemail.constantcontact.com/PRESS-RELEASE.html?soid=1125761508982&aid=7E5PGfld1Io

The Hama Health Directorate also published a video with doctors explaining the symptoms of the victims, consistent with organophosphate poisoning, which would include Sarin:

The Hama Health Directorate video also contains statements from victims of the attack, explaining how a war plane dropped the bomb filled with the poison gas on Al Lataminah

Bellingcat also contacted health care workers who treated victims of the March 30th 2017 attack in Al-Lataminah, who sent us 3 additional videos showing victims.

Bellingcat also contacted Anwar Rahmoun, the farmer interviewed by Human Rights Watch, who provided more details of the attack https://www.bellingcat.com/news/mena/2017/10/26/investigating-march-30-2017-sarin-attack-al-lataminah/

Anwar Rahmoun also provided Bellingcat with the following video, showing one of the victims who was reportedly treated for 3 months in Turkey returning to Syria

We also spoke to other witnesses, who stated the location of the attack was a field on the south of the town, near a rebel headquarters, and the victims were a mix of fighters and civilians, some of whom were working the fields at the time of the attack.

A few videos were filmed and uploaded showing the impact site, such as this video from Halab Today TV, which allowed us to geolocate the impact site.

We were able to geolocated the impact site of the March 30th attack to a site south of Al Lataminah, consistent with other statements about the attack. The significance of this particular area became clear after the publication of the OPCW FFM report on the March 24th attack.

The June 2018 OPCW FFM report contained details of a previously unknown Sarin attack that occurred on March 24th 2017, including the exact location, just north of the impact site of the March 30th attack.

Surprisingly, the March 24th attack, which the OPCW FFM report said involved Sarin, was totally unknown at that point. Bellingcat was unable to find any open source information about the attack, and the OPCW FFM discovered it during its investigation of other attacks.

But why was this particular location targeted in two Sarin attacks just days apart? The likely target was an underground opposition HQ, previously targeted by Russia, as shown in this video, where it's incorrectly described as an ISIS base in Raqqa

This brings us to the type of munition used in the March 24th and March 30th attacks in Al Lataminah. In the June 2018 OPCW FFM report they made a point of the similarities of the Sarin used in those attacks and Khan Sheikhoun on April 4th 2017

This is significant, as the OPCW-UN JIM stated key indicator chemicals in the Sarin used in Khan Sheikhoun indicated it was produced as part of the Syrian government's Sarin production process. Those same markers may be part of the OPCW IIT report published today.

While there's no open source images of the bomb debris from the March 24th attack, there are images of the debris from the March 30th attack, and they provide another interesting connection to the Khan Sheikhoun April 4th 2017 attack.

A type of filling cap photographed at the site of the Khan Sheikhoun attack, and described by the OPCW UN JIM as uniquely consistent with Syrian chemical bombs, was also documented at the March 30th attack site in Al-Lataminah.

Unlike Khan Sheikhoun, much more debris was documented at the Al-Lataminah March 30th site, and over two years Bellingcat worked to establish the exact type of bomb used in Al-Lataminah, eventually establishing it was an M4000 chemical bomb.

It took us until September 2019 to discover a video of the same type of bomb, which we were able to measure and compare to the debris at Al-Lataminah, confirming the identification of the bomb as an M4000 https://www.bellingcat.com/news/mena/2019/09/24/the-first-images-of-the-type-of-chemical-bomb-used-in-syrias-sarin-attacks/

One major question about the March 24th 2017 attack is if debris was recovered and documented, and that's detailed enough to allow the bomb to be identified. It's likely we will find out in today's OPCW IIT report.

Along with the March 24th and March 30th 2017 Sarin attacks, the OPCW IIT is also investigating a March 25th 2017 chlorine attack in Al-Lataminah, which we've also investigated https://www.bellingcat.com/news/mena/2017/10/09/summary-open-source-evidence-march-25th-2017-chlorine-attack-al-lataminah-hama/

That attack hit the entrance area of an underground hospital, filling the structure with chlorine gas, forcing staff and patients outside and exposing them to chlorine gas

This tweet from the White Helmets included photographs from the attack, and one of the victims, Dr Ali Darwish, who later died. https://twitter.com/SyriaCivilDef/status/845712375462420480

Dr. Basel Termanini, Vice-President of @sams_usa explained that Dr Darwish was operating on a patient when the attack occurred, and refused to leave without closing the patient, but as a result was exposed to a lethal amount of gas

That's all for now, but Bellingcat's @EliotHiggins will be live-tweeting the release of the OPCW IIT report, posting relevant open source material, and highlighting significant parts of the report.