Two extracts from:
The Nerve Gas Agent Attack in Khan Shaykhun, Syria: A Quick Turnaround Assessment of the White House Intelligence Report Issued on April 11, 2017 by Theodore A. Postel, Professor Emeritus of Science, Technology & National Security Policy, Massachusetts Institute of Technology, 12/4/17 (unz.com):
"I have reviewed the [White House statement claiming intelligence findings about the nerve agent attack on April 4, 2017 in Khan Shaykhun, Syria] carefully, and I believe it can be shown, without doubt that the document does not provide any evidence whatsoever that the US government has concrete knowledge that the government of Syria was the source of the chemical attack in Khan Shaykhun, Syria... In fact, a main piece of evidence that is cited in the document points to an attack that was executed by individuals on the ground, not from an aircraft, on the morning of April 4 [...]
"[W]hat the country is now being told by the White House cannot be true and the fact that this information has been provided in this format raises the most serious questions about the handling of our national security."