The U.S. government insists it has the intelligence to prove it, but the American public has yet to see a single piece of concrete evidence no satellite imagery, no transcripts of Syrian military communications connecting the government of President Assad to the alleged chemical weapons attack last month that killed hundreds of people.

In the absence of such evidence, Damascus and its ally Russia have aggressively pushed another scenario: that rebels carried out the August 21 chemical attack. Neither has produced evidence for that case, either. That’s left more questions than answers as the U.S. threatens a possible military strike.

The early morning assault in a rebel-held Damascus suburb known as Ghouta was said to be the deadliest chemical weapons attack in Syria’s two and a half year civil war.

Survivors’ accounts, photographs of many of the dead wrapped peacefully in white sheets shocked the world and moved President Barack Obama to call for action because the use of chemical weapons crossed the red line he had drawn a year earlier.AP