Reports from Syria indicate that a chemical substance has been used in Idlib in a horrific attack.
As with the now-infamous Sarin attacks in August 2013, there are numerous accounts, including gruesome video, that allege that prohibited nerve agents have been used.
Previous incidents involving Sarin have demonstrated that diagnosing nerve agent exposure by examining video clips is problematic.
Many signs of exposure are not easily recorded, and given the extreme lethality of all of the nerve agents, most victims who make it alive to the care of a medic do not necessarily display the most grave signs and symptoms.
Exposure to liquid nerve agents (all of them are liquids, not gases, at normal temperatures) causes effects that appear in somewhat different chronology to those of victims that inhale vapours.
However, all of the nerve agents behave the same in terms of their physiological effects on the human body.
The weapon used may not have been Sarin. It could plausibly have been one of the other nerve agents.
Documents released by the Organisation for the Prohibition of Chemical Weapons (OPCW) show that the Assad government had the ability and supply chain to produce VX, a nerve agent that is a non-volatile liquid that can cause contamination that can last for weeks or months.
Another possibility is Tabun, which was manufactured in great quantities in Iraq during the Iran-Iraq war.
Tabun has the advantage of being easier to manufacture, and it is marginally less lethal than Sarin or VX. However, it is orders of magnitude more lethal than chlorine, which has been prolifically used.
Other nerve agents are possible but unlikely, as they get into exotic chemistry and strange methods of production.
Only a serious effort to collect, preserve and analyse forensic evidence will definitively identify the material used. Finding the remains of the actual weapon(s) used will be critical to this effort.
The use of nerve agents, if proven, raises serious implications. It will represent a grave escalation beyond the chlorine which has been routinely used.
Perhaps the lack of punishment for using chlorine, combined with chlorine's relatively low lethality, has driven this escalation.
Use of nerve agents by the Assad government also would demonstrate that either the Syrian state was not honest in its declarations when it joined the Chemical Weapons Convention (CWC) and OPCW, or that it has re-established both a supply chain and a manufacturing capability that it had formally renounced.
The issue of where the precursor chemicals come from amidst sanctions is of concern.
Chemical arms control appears a lost cause in the Syrian civil war, but also the international failure to enforce treaties damages arms control in the future.
Chemical weapons, Sarin and others disproportionately punish civilians, particularly the young and old, and disrespecting chemical warfare bans sets a horrible precedent.
Dan Kaszeta is a London-based consultant. He is a former US Army Chemical Corps officer and has worked in chemical defence issues for over 25 years, including assignments at the White House Military Office and the US Secret Service. Follow him on Twitter.