Jean-Marc Ayrault
“The perpetrators of the Khan Sheikhoun atrocities and other chemical attacks will be held accountable for their criminal acts, not only in the courts but also the history books.”
-Jean-Marc Ayrault — French Minister of Foreign Affairs
The French government released a report blaming the Syrian government for this month's chemical weapons incident.

The report states:
According to the intelligence obtained by the French services, the process of synthesizing sarin, developed by the Scientific Studies and Research Centre (SSRC) and employed by the Syrian armed forces and security services, involves the use of hexamine as a stabilizer.

***
The presence of the same chemical compounds in the environmental samples collected during the attacks on Khan Sheikhoun on 4 April 2017 and on Saraqib on 29 April 2013 has therefore been formally confirmed by France. The sarin present in the munitions used on 4 April was produced using the same manufacturing process as that used during the sarin attack perpetrated by the Syrian regime in Saraqib. Moreover, the presence of hexamine indicates that this manufacturing process is that developed by the Scientific Studies and Research Centre for the Syrian regime.
Sounds convincing, right? But the report falls apart upon closer scrutiny ...

Specifically, the head of the United Nations' team investigating the possible use of chemical warfare in Syria (Åke Sellström) wrote an email to MIT rocket scientist Ted Postol in 2014 stating:
Hexamine ... is a product simple to get hold of and in no way conclusively points to the [Syrian] government. In addition, hexamine found in samples may be derived from other sources for example, explosives.
Sellstrom to Postol
© unknown
(I blacked out Postol's email address to protect his privacy; as I did with personal information in the email below.)

This week, Washington's Blog wrote the following email to Dr. Sellström seeking confirmation:
The Washington Post quotes French officials as saying that analysis of sarin from Khan Sheikhoun shows the presence of hexamine, indicating that the sarin was produced by the Syrian government:

However, my understanding is that it is easy to acquire hexamine, and so the presence of the substance does not indicate state-sponsored manufacture. I also understand that hexamine is a common byproduct from explosives. Is that right?
Dr. Sellström responded:
It is really a question of the meaning of the word indicating. The presence of hexamine could, indeed, indicate that the source is the government. Leaving out who actually used it.

But it could also indicate a lot of other things, like someone using the same recipe for example
Sellstrom 2
© unknown
In other words, the lead UN investigator is saying that the presence of hexamine could prove that:
(1) The Syrian government did use sarin

(2) The rebels got a hold of old stocks of government-produced sarin, and then used it themselves

(3) Someone reverse-engineered the sarin formula previously used by the government and created their own new sarin

(4) Something else altogether (e.g. that the hexamine came from every day explosives, was otherwise introduced from other sources, or perhaps the evidence was altogether fudged for political purposes)
The French report also claims:
France assesses that the theory of an attack by the armed [rebel] groups using a neurotoxic agent on 4 April is not credible. France has no information confirming the possession of sarin by these groups.
That's downright silly, given that it was long ago shown that the rebels do possess chemical weapons such as sarin.