And the Rain Came Falling



This is a draft excerpt of what will eventually form part of my analysis of the chemical weapons attack on Ghouta, Damascus, on August 21, 2013. It is also a thought experiment initially conceived as a means of bringing to wider public attention the circumstances of what is known as the “Yellow Rain” affair – events that have become one of the foundational case studies in the field of chemical weapons research and analysis.

The original intention was to copy, reorder and, to some extent, summarize and rework the narrative of the “Yellow Rain” affair published by Mathew S. Meselson and Julian Perry Robinson in their joint effort entitled “The Yellow Rain Affair: Lessons from a Discredited Allegation,” and to put it in a format akin to an executive summary. The hope was that this exercise would generate a discussion of parallels between the lessons learned from the events of last century and the circumstances in which we find ourselves today when we consider the incident in Ghouta and its ongoing investigation.

A word of caution and clarification is necessary, however – the differences between the “Yellow Rain” affair and the events that occurred in Ghouta, and the investigation that followed, are vast. There are significant factual divergences, and the CBW compounds alleged to have been at play are nothing like one another. This discussion is not meant to insinuate that there are conspiratorial undercurrents that unite the two narratives.

As indicated above, the intent was to highlight the vital methodological, procedural and forensic lessons learned in the aftermath of the “Yellow Rain” affair and to ask the reader to ponder the events and the investigation in Ghouta in light of these lessons. I invite the reader specifically to consider, in light of the likely outcome of neglecting the lessons once learned, their importance for our understanding of the incident in Ghouta.

Throughout this excerpt, I have very liberally used the “Yellow Rain Affair: Lessons from a Discredited Allegation” piece by Meselson and Robinson, although I have tried to indicate where I am quoting directly from the original text. In the latter section, I refer primarily to the “Alleged Chemical Weapons in Syria”, a Harvard Sussex Program Occasion Paper by Julian Perry Robinson, accentuated by a methodological appendix prepared by Meselson. I have not provided proper citations at this time.



Charges of War Crimes

The charges of CBW use in Laos and Cambodia were trumpeted in the month and year of my own birth. “[In September 1981], U.S. Secretary of State Alexander Haig … charged Soviet-backed Laotian and Vietnamese forces with waging toxin warfare against Hmong resistance fighters and their villages in Laos and against Khmer Rouge soldiers and villages in Cambodia.”

  • (Alexander Haig, U.S. Secretary of State, address in West Berlin, September 13, 1981
  • U.S. Department of State, Special Report no. 98, “Chemical Warfare in Southeast Asia and Afghanistan,” March 22, 1982.)

The allegations were quickly brought to the attention of the United Nations. “[In November 1982,] the charges were repeated with additional details  in  [1] a  further  report  to  the  Congress  and [2] to  the  member  states  of  the United Nations.”

  • (U.S. Department of State, Special Report no. 104, “Chemical Warfare in Southeast Asia and Afghanistan: An Update,” November 11, 1982.)

Public Statements and Allegations

Following the initial accusations in the fall of 1981, in 1982, scientists examined “at least 100 samples of yellowish spots and powders from alleged attacks in Laos and Cambodia … under the microscope and, without exception, found [them] to consist principally of pollen.” Pollen became the compound of interest. Expert analysis and studies quickly followed.

In November 1982, Gay Crocker, a State Department CBW Intelligence Officer, stated that the pollen found in Laos and Cambodia was:

“commercially collected [and] the right size to be retained in the body [of a human being].”

  • (Gay Crocker, a State Department intelligence officer who chairs the Assessments and Policy Support Sub-group of the CBW/Toxin Use Working Group)

The US began to build its case build that pollen was the delivery mechanism for CBW compounds.

Shortly thereafter, Sharon Watson, U.S. MIIA Intelligence Analyst, stated that the pollen found had:

“secondary aerosol effect that can be caused by kicking up this pollen-like dust that is of a particle size that will be retained in the bronchii of the lung … a very effective way of getting [trichothecene mycotoxins] across”

Watson further insinuated that, as a CBW delivery mechanism, pollen was a “very clever, clever mixture.”

  • (Sharon Watson, an intelligence analysis at the U.S. Army Medical Intelligence and Information Agency (MIIA), later the Armed Forces Medical Intelligence Center (AFMIC))

In December 1982, Kenneth Adams, the US Deputy Representative to the UN, in an address to the United Nations, stated the following:

“We are now, however, able to isolate the components of yellow rain … There is good evidence for the presence of commercially produced pollen as a carrier and to help ensure the retention of toxins in the human body.”

  • (Kenneth Adelman, then U.S. Deputy Representative to the UN, in a December 1982 address to the First Committee of the United Nations General Assembly)

Expert Reports

The expert reports prepared ultimately prepared in the course of the investigation triggered by the US allegations (briefly, the Haig and Shulz reports), were adamant that the identified pollen was contaminated with CBW, and was used as a CBW delivery mechanism. This killer pollen became known as the “Yellow Rain.”

The reports cited three main types of evidence in support of the “Yellow Rain” allegations:

  1. WITNESS INTERVIEWS of Hmong villagers describing some 400 alleged attacks between the 1975 and 1982;
  2. SAMPLES OF ALLEGED CBW, provided by people who claimed to have witnessed attacks and who stated that the samples were air-dropped poison: the so-called “Yellow Rain”; and,
  3. CHEMICAL ANALYSES confirming the presence of trichothecene mycotoxins in:
  • environmental samples from sites of alleged chemical attack;
  • biomedical samples from individuals allegedly exposed; and,
  • tissue taken at autopsy from a Khmer Rouge soldier.

Further, the Haig report cited an account given to U.S. Embassy personnel in Thailand by a Lao pilot who had defected and who, according to the report, had been directly involved in chemical warfare. This account remained uncorroborated and was later confirmed to be mostly a fabrication.

It is important to note that this mysterious pollen was ultimately conclusively determined by an outside specialist that had no relation to the area of CBRN studies and research to be bee feces.


According to Meselson and Robinson, “all  of  the  evidence  adduced  at  the  time  that  is  now public, including a large body of material declassified and provided to [them] starting in 1986 under the Freedom of Information Act supports explanations of the Yellow Rain events that involve no CBW weapons at all, beyond the use of riot-control agents.”

In other words, the so-called “Yellow Rain” was nothing more than bee feces, and had no CBW component. Both conclusive chemical weapons reports, that had confirmed presence of CBW in dozens of samples, turned out to be entirely baseless.

Furthermore, it appears that, even at the time the charges were made, and the Schultz and Haig reports were issued, the allegations were already unsustainable for a number of reasons, including the fact that the alleged CBW delivery mechanism had no such tendency to disperse as was being alleged.

According to Meselson and Robinson, from their review of subsequent attempts to confirm the conclusions of the Haig and Schultz reports,  the U.S. accusations had no credible evidence to support them:

  1. no credible or confirmed witness reports;
  2. no confirmation of an association between trichothecenes and any alleged attacks;
  3. all environmental and biomedical samples found to contain trichothecenes were false positives;
  4. no evidence in the form of a recovered  rocket  or  other  munition carrying trichothecenes;
  5. all claimed tricothecenes symptoms resulted from causes other than CBW; and
  6. no credible confirmatory defector or prisoner testimony emerged since.

For the authors, therefore “counterfactual analysis leads to the conclusion that, except for riot-control agent, CBW weapons were not used in Laos or Cambodia.”

In addition, Meselson and Robinson concluded the following regarding the “Yellow Rain” investigation:

  1. it failed to employ reliable methods of witness interrogation;
  2. it failed to employ reliable forensic laboratory investigation;
  3. it was marred by the dismissal and withholding of contrary evidence;
  4. it was undermined by the lack of independent review; and,
  5. under independent scrutiny, the evidence collected could not be confirmed or was discredited.

Despite the thorough debunking of the “Yellow Rain” claim, the US charges – that CBW were used – were not withdrawn, even when the allegations proved unsustainable.


To Meselson and Robinson, the lessons to be learned from the Yellow Rain episode are straightforward:

(1)    Reliable procedures must be used to acquire and evaluate interview evidence, including:

  1. the use of corroborative cross-checks and double-checks; and,
  2. careful avoidance of leading questions.

(2)    Chemical identification of trace components must adhere to appropriate standards for forensic analysis.

(3)    Results of chemical analyses must be corroborated by an independent laboratory.

(4)    Hypotheses must be subjected to wide consultation and objective criticism.

The authors conclude as follows:

“Failure to apply these lessons, whether through incompetence or because of political exigencies and pressures, imperils the credibility of subsequent investigations of situations in which CBW weapons may actually have been used.”

(I have taken out an extensive discussion of what went wrong with the “Yellow Rain” investigation – anyone interested should refer to the relevant articles, and I am happy to provide same from what I have collected so far)


Writing in the summer of 2013, in his analysis of numerous alleged instances in which chemical weapons were used in Syria, Robinson raised many of the same criticisms he made in his commentary on the “Yellow Rain” affair.

The lack of specificity in the Western governments’ briefings on the subject was one of them. Robinson made the following point:

“[T]he pressing task of demonstrating whether there is or is not truth in the allegations necessitates more evidence than bald assertion.”

He went to conclude:

“It is not at all obvious why, [the] governments have not:

[1] publicly described

[2] for scientific audiences

[3] the analytical methods they applied to

[4] the physiological (and perhaps other) samples

[5] in which they all say they have found sarin.”

Robinson’s answer to his own question is disconcerting:

“Possibly political authorities in the accusing countries have been unable accurately to judge the reliability of chemical analytical reports.”

As a result, he turned to credibility, rather than reliability, as a yardstick for measuring the strength of the allegations that were being made prior to the August 21, 2013 incident:

“[R]ecognising that the truth is not yet available [let us] focus instead on the question of credibility.”

In considering the usefulness of a credibility assessment, it is critical to consider the methodology that would support its use. How does one determine credibility outside the confines of a court of law and the strictures of common law practice?

Although I would argue that, where crimes, whether domestic or international are alleged, legal standards are the only applicable tools, Robinson does have a point about the court of public opinion.

“The existence of the better explanation makes it that much easier to believe the allegations.”

Robinson makes an excellent point, when he says that it is not plausible to argue that Syria’s alleged use of chemical weapons is a manifestation of Syria’s campaign to probe “the resolve of the outside powers who might intervene.”

On the other hand, the alternative explanation, that the small-scale use of chemical weapons witnessed prior to August 21, 2013 is guided by Syria’s new CW-use doctrine to

“incapacitate rebels and force them out of strategic areas, while keeping deaths among their ranks limited”

fits neatly into the logic and factual, tactical and strategic matrices of the Syrian civil war.

This account largely fits all previous incidents of alleged CW use (with the exception, possibly, of the Khan-al-Assal event). It does not describe the logic of the incident that occurred in Ghouta on August 21, 2013.

The Ghouta incident was neither “small-scale”, nor did limit the number of deaths among the rebels or the civilians (if mainstream accounts of the death toll are to be accepted as accurate). It does not appear to conform with the posited limited use doctrine.

Moreover, the Ghouta attack appears tailor-made to put the resolve of outside powers to the ultimate test. In other words, it seems to be designed to do what seemed implausible a mere few months ago.

We are left wondering what “better explanation” would make it “easier to believe the allegations” being made against the Assad regime in relation to the August 21, 2013 attack.

The fact is, those explanations may well exist:

(1)    It could have been an accident.

And yet, military accidents usually result in deaths among the attackers, rather than those being attacked. Moreover, an attack on the scale being alleged to have occurred in Ghouta required substantial preparations. The necessity of substantial preparations eliminates the possibility that the attack was accidental or unintentional.

(2)    It could have been a miscalculation.

However, if some plausible calculations of the total volume of Sarin deployed in Ghouta (such as, for instance, an estimate put forward by Dan Kaszeta) are to be believed, a theory that would posit a miscalculation involving one (1) ton of Sarin is simply not credible.

(3)    It could have been a rogue element in the regime, such as

(a) Assad’s brother, who is believed by many to be a psychopath capable of mass murder (or possibly plotting to supplant his commander-in-chief);

(b) a rogue faction either desiring to trigger a war with the United States, a doomsday-scenario on the scale of what Aum sought to perpetrate in Japan; or

(c) a rogue group seeking to undermine the Syrian regime.

Neither scenario passes the litmus test of “better explanation” that would cement the foundations of its credibility. Throughout the crisis, Assad retained unchallenged control over his government and military apparatuses, and all signs suggest that he has further reinforced his grip on power since.

No challenger, individual or group, emerged to contest Assad’s dominance and seize the opportunity to stage a coup in the immediate aftermath of the August 21, 2013 attack, when Assad’s power was at its weakest, or has appeared since.

Even if we accept that the there was no opportune moment, and that the crisis was rapidly overcome, there were no signs of or conditions that would foment dissent in the Syrian regime prior to August 21, 2013. In fact, the military gains made by the SAA prior to the Ghouta attack would have dissuaded any misguided attempt at an internal rebellion. The Syrian regime would face extinction if it were to fracture. Its relentless march against the rebels and its own citizens is what has maintained its integrity to date.

Seeking the solace of credibility in arguments reliant on idiosyncratic pathologies of one individual or on myopically alien fantasies of an ultra-hawkish group thirsting for a showdown with the world’s remaining superpower is beyond the confines of these ruminations.

Other arguments may well fit the bill, but they are not immediately apparent. The fact is, the August 21, 2013 attack is difficult to reconcile with the mostly neat (however monstrously so), even-keeled, methodical, and doctrinal approach of small-scale CW incidents described by Robinson.

To an impartial observer this assessment would suggest that the August 21, 2013 incident stands alone (nothing more, for the moment) – it does not fit into the existing pattern of CW use, nor can it be explained using existing models of warfare in the Syrian civil war. Nor does it have its own, inherent, “better explanation” that would allow us to disregard the question of reliability of evidence in favour of credibility of a meta-explanation, in the manner proposed by Robinson.


As a result, we are left with physical evidence collected by the UN investigators as the only tool that we can rely on in the court of public opinion. The foremost requirement of evidence at law is reliability. Unreliable evidence is not admissible, and no exception exists to circumvent this basic rule.

We have already examined the requirements of reliability discussed by Meselson and Robinson in relation to the “Yellow Rain” affair. Robinson’s consideration of the Syrian example betrays no change in his opinion. Meselson’s appendix to the paper makes the following points (drawn, again, from the lessons learned in the aftermath of the “Yellow Rain” investigation, as well as from practices developed by the OPCW):

  1. even highly regarded national laboratories participating in the Official Proficiency Tests overseen by the Technical Secretariat of the Organization for the Prohibition of Chemical Weapons (OPCW) have, on occasion, reported false positives and false negatives. (a fact that can be verified conclusively by perusing the Technical Directorate’s periodic Performance Assessment reports); and,
  2. to have high confidence in laboratory evidence for the presence of Sarin or other chemical warfare agents or their distinctive breakdown products in environmental or biomedical samples, the following is mandatory:

High Confidence Analysis

  1. Use of multiple laboratories (of which there should be at least two and preferably three) is required.
  2. All participating laboratories must conclude without reservation that the agent or its distinctive breakdown products are present in the provided samples.
  3. The laboratories used must have excellent prior records in such analysis.

Blanks and Controls

  1. The analyses must include suitable blank samples and control samples in matrices similar to those of the field samples.
  2. The blanks and controls should be provided by an outside laboratory (one not doing the analyses).
  3. Analyses of blanks and controls should be interspersed with analyses of the environmental and/or biomedical samples of interest.
  4. The identity and provenance of all samples should be unknown to the laboratories doing the work.


  1. Laboratory findings should be based on two different generally accepted methods of analysis based on different physical principles.

Independent Review

  1. Laboratory methods and findings should be reviewed by an independent group of technically qualified and experienced experts with unimpeded access to laboratory personnel who had done the analyses and to their laboratory records.
  2. High confidence requires unanimous approval by the review group.

Implicit in these requirements is that the entirety of information regarding the analysis performed must be made available to the public and to those performing independent review. This includes:

  1. complete information regarding methodology used;
  2. complete data received as a result of analysis performed; and,
  3. complete description of the processes and verification mechanisms.

The fact is, most of the methodology outlined by Meselson has been ignored by the UN, starting with the use of blanks, and ending with the “high confidence analysis” – the requirements of the latter have not been met by the vast majority of environmental samples that have been analyzed. Even where it has been complied with in form, only the bare minimum was fulfilled. And, as a result of complete lack of transparency about methodological processes and data, the results submitted by the UN are unverifiable.

Based on the rules expounded by OPCW, in its Appendices, the directives of it Technical and Scientific Directorates, and other methodological discussions that exist in literature, we are entitled to conclude:

No evidence currently at play, whether supplied by the UN, NGOs, or national governments meets the legal requirements of reliability.

Nor does the available evidence meet the standards of reliability proposed by Meselson and Robinson in their “Yellow Rain” discussion or in Robinson’s recent overview of CW use in the course of the Syrian civil war. The reason is simple – virtually every one of their recommendations has been disregarded by the investigators, including those appointed by the UN and OPCW.

What is unfortunate is that we do not know whether the analyses performed were scientifically sound. What we do know is that there is no transparency to the evidence being presented.

Meselson and Robinson do not go into detail about methodology and science in their discussions. Their direct involvement in the “Yellow Rain” affair taught them one critical rule, a lesson we would be well served to heed:

Evidence that is not transparent is evidence that is not reliable.

And, as we know from the mandates of legal process and substantive law, unreliable evidence is no evidence at all. Where no evidence exists, there is no case, however difficult that may be to accept for those of us who cannot countenance war crimes and crimes against humanity going unpunished.

What is even more disturbing is the answer Robinson gives to why evidence that led by Western governments has been so lacking in scientific data, description of methodologies, and explanation of procedural techniques:

“Possibly political authorities in the accusing countries have been unable accurately to judge the reliability of chemical analytical reports.”

When the UN investigators fail to include the data they found and discuss the analytical methodologies they used, are we to conclude they also “have been unable accurately to judge the reliability of [their] chemical analytical reports”?

Moreover, and more globally, in the absence of a credible explanation of what happened on August 21, 2013, and faced with lack of reliable evidence, we are powerless not only to make decisions that are ours to make, but also to understand the decisions being made on our behalf.


The Yellow Rain Affair: Lessons from a Discredited Allegation

by Matthew S. Meselson and Julian Perry Robinson

Alleged Use of Chemical Weapons in Syria

by Julian Perry Robinson

Harvard Sussex Program Occasional Paper, Issue 04, June 26, 2013