Assad is a guy who got his education from medical schools in Syria and UK, and is considered well read and tech-savvy. He knows well that if he starts using poison gas or anything that could immediately provoke international attention, US and UN will come after him and easily dethrone him. Why in the world would this guy actually use the toxic gas and order a hit on UN inspector?
Are these attacks initiated by Assad or are these by people who want to frame Assad so that US has enough reason to invade Syria? I will leave the answer to you.

In noway I am justifying Assad's deeds; however, he also cannot be this stupid to be pulling a lion's tail like this.