The truth is the first thing do die in war. Now, I don't don't know who used the gas but what I find sort of interesting is that people where dying and killing each other before and now that they use another type of weapon to kill each other it's somehow more atrocious. Killing is killing regardless of what you use and just the word chemical weapon is interesting since there is chemicals in most bullets and I remember the Vice short about US bombs/bullets with (I believe) uranium in them.
As for US intervention, I think ground troops is out of the question. The most likely thing we will see is something similar to what happened in Libya.