here is a little history, taken from an article.

"The U.N. thoroughly investigated the first 2013 attack. The U.N Commission of Inquiry’s Carla Del Ponte ultimately said the evidence indicated the attack was carried out by the Syrian rebels — not the Syrian government. Despite this, support for the Syrian rebels from the U.S. and its allies only increased, raising serious questions about Obama’s sincerity when condemning chemical attacks.
Pulitzer-Prize winning journalist Seymour Hersh found the second major attack was committed in a similar manner. Hersh found that the U.S. quite deliberately attempted to frame the evidence to justify a strike on Assad without even considering al-Nusra, a terror group with access to nerve agents that should have been a prime suspect."

just keeping this in mind is all.