Trump previously bombed Syria because, it was alleged that President Bashar al-Assad used chemical weapons, such as gas: https://www.nytimes.com/2017/04/04/world/middleeast/syria-gas-attack.html?_r=0. There have been numerous critiques of this, not just from the fringes, but even more mainstream sources: http://www.zerohedge.com/news/2017-04-08/michael-savage-turns-trump-says-syrian-gas-attack-was-false-flag-operation, and of course, Putin denies that chemical weapons were used.
Now, moving on from gas, the latest claim is that Syria is now operating genocidal ovens, burning the dead: http://thehill.com/blogs/pundits-blog/international-affairs/334161-syrias-crematoriums-echo-the-holocaust-president. “The most important human rights story of the week seems to have been largely overshadowed by political headlines. The report that should consume the international community is the revelation that U.S. satellite photos have identified crematoria at Syrian President Bashar Assad’s Sednaya prison. Assad built these killing centers to destroy the evidence of his mass murder of innocent civilians and political opponents in Syria, amid a growing genocide.”
See: https://www.washingtonpost.com/world/national-security/us-accuses-syria-of-mass-executions-and-burning-bodies/2017/05/15/b7b66c86-3986-11e7-8854-21f359183e8c_story.html?utm_term=.bf55cc2006fe.