The US Government Assessment

If this is your first time here, I recommend starting from the conclusion page.

After reviewing the UN report in my previous post, I will now examine the US Government Assessment published August 30th.

According to the report, the US Government has high confidence that a nerve agent attack was carried out by the Syrian regime. Since there is little dispute that sarin was used in the attack, I will focus only on the evidence connecting the Syrian regime to the attack. This is based on several pieces of evidence:

1. Personnel related to chemical warfare were preparing chemical munitions prior to the attack.
2. Regime elements took protection against chemical attacks on the day of the attack.
3. The regime launched a rocket and artillery attack prior to the mass poisoning. The report specifically mentions detecting an attack 90 minutes before chemicals were reported on social media.
4. After the attack "a senior official ... confirmed that chemical weapons were used."
5. An order given to chemical weapons personnel to cease operations after the attack.
6. Increased shelling after the attack.
7. An assessment that the Syrian opposition did not use chemical weapons.
8. No indication that the opposition carried out a large scale rocket and artillery attack. 

When viewed together the evidence seems overwhelming. However, when examining each claim in detail, they turn out to be deeply flawed.

Before reviewing the evidence, it is important to note that this is not an objective document. It is titled 'Government Assessment', rather than 'Intelligence Assessment', and is likely to be affected by political interests. This is made obvious when examining its structure: It does not follow a process of providing several hypotheses, showing how each is supported or refuted by evidence, and then analyzing which is the most likely. Instead, it starts with the assessment and then provides only supporting evidence.

We should therefore assume that evidence is presented or interpreted in the report in a biased fashion.

So now let's examine the evidence:

Items 1 and 6: These are circumstantial evidence attempting to show activity related to chemical warfare before and after the attack. By its nature, the strength of circumstantial evidence is probabilistic, and its strength cannot be assessed out of context. An objective analysis should include information such as the frequency at which such activities occur in other periods, and activities that could have been associated with a chemical attack but were not detected.

The US and its allies probably collect millions of data points in Syria every day. In these amounts of data almost any desired pattern can be detected - especially when a large organization is under pressure to provide such a result. Without a full statistical analysis this kind of evidence carries no weight.
Update: In this report (minute 2:04) we are told: "US Intelligence detected activity at known Syrian chemical weapons sites in the days before the attack. At the time that did not appear out of the ordinary”. This is another indication that the circumstantial evidence is probably not statistically significant.

Item 2: This also suffers from the limitations of circumstantial evidence, but it could also be explained as protective measures against a rebel chemical attack. The report attempts to refute this thesis by claiming "our sources did not detect any indications ... that opposition affiliates were planning to use chemical weapons". Of course, the fact that the US did not detect such a threat does not mean such an attack was not being planned, nor that the Syrian army does not view it as a possibility that should be prepared for. Specifically, the regime has declared numerous times that its troops are being attacked by chemicals (a few examples here). Even if we assess this is a conspiracy to gain international support, it is still likely to be accompanied by chemical warfare protection to the troops.

Item 3: The regime immediately admitted to carrying an attack in these areas. However, the report attempts to draw a correlation between the landing locations of regime rockets and the locations of chemical poisoning, implying at a chemical attack distributed over a vast area. To strengthen this claim the report contains the following map:

If this was indeed true, it would point to a massive attack that is much more likely to have been carried out by the regime. However, in the following days it became evident that the chemical attack occurred in a small area in the neighborhood of Zamalka, and all eyewitness reports originate from this area. As noted in the disclaimer attached to the map, reports from other locations are a result of patient evacuations to nearby hospitals. The report chose to ignore this disclaimer and create the impression of a chemical attack spanning 10-20 km. This was echoed in the President's Speech on September 10th:

"They fired rockets from a regime-controlled area into 11 neighborhoods...Shortly after those rockets landed, the gas spread."

Note: The area of Moadamiyah is also reported often as suffering from a chemical attack. This has been shown to be unreliable.

The report also states that rocket launches in regime territory were detected 90 minutes before chemical reports surfaced in social media (Update: according to this interview this is based on satellite detection of rocket flashes in regime areas). As many people already noted, this is actually evidence against a regime attack. The effects of sarin are felt instantly, and it's fair to assume that within minutes panic spread. It seems unlikely that for 90 minutes not one of the thousands of people in the area thought to warn their friends.

Update: The first report of the chemical attack in social media was at 2:26 AM, while eyewitnesses later reported that the shelling happened at around 2:00 (which would make for a much more reasonable time delay). This shows that the flashes detected by US satellites at regime-held areas happened before 1:00 AM and are therefore not related to the chemical attack. 
Update 2: 'Heavy fighting' was reported on social media at 1:15, which would again indicate a conventional attack occurring before 1:00. So it now seems clear there was a government conventional attack before 1:00, and a separate chemical attack at 2:00.

Item 4: This is one of the strongest pieces of evidence in the report. Unfortunately, it was not shared and there is no way to assess its reliability. Presumably this is done to "protect sources and methods", but something doesn't add up here: Enough information is given on this call (also here) to allow Syrian counter-intelligence to start an investigation that will determine who were the speakers and estimate how it was intercepted. Providing direct quotes (without identifying information) will not assist Syria's investigation and therefore not damage sources.

Which leaves us with a more plausible explanation as to why no quotes are given: Like other evidence in the report, this call was interpreted very generously, and did not contain any incriminating evidence.

This is also the claim made here, but without providing the source. If anyone has more information to help clear this up, please share.

Item 5: Given the international response that the Ghouta videos created, it is not surprising that the government put the brakes on many activities until they figured out what happened.
Update: Another explanation is that this was an order to stop use of riot control agents, which the regime is known to have used (more details here).

Item 7: This assessment is not accompanied by any evidence. It is analyzed in detail here. 

Item 8: This assumes the chemical attack indeed involved a large scale rocket attack, which was refuted above. Additionally, the report doesn't state how accurate their coverage of the area is - specifically, what is the probability of detecting such a rocket attack.

See here more holes in the US Assessment, from Associated Press.

Update: The report states "We will continue to seek additional information to close gaps in our understanding of what took place.". However, after 2 months no additional information was presented. It is safe to assume that if strong evidence was found, it would have been presented.

Update 2: Seymour Hersh has published objections from within the US Intelligence to the Government Assessment. It is discussed here.

Conclusion: The US Government assessment provides overall weak evidence, with some of the evidence strengthening the regime attack theory and some weakening it.

Did I miss anything? Please share your evidence and analysis and help me improve my conclusions.