So who sent the gunman, assuming he didn't act on his own? Given the he cited Aleppo, he is likely from one of two factions. 

The smaller faction by far is the so-called Syrian Free Army. They are said to have about 15,000 fighters. These are the 'moderate' rebels that you frequently hear about. The larger group, about 45,000 fighters strong, is the Islamic Front. It's manifesto is to completely destroy the Syrian government and establish an Islamic state in Syria. (Funny how you never hear about them, isn't it?) Islamic Front was created in 2013 out of six militant groups. It claims no affiliation with either Islamic State or al Qaeda/al Nusrah, in order to avoid being designated a terrorist organization. However it has exactly the same goals as those two terrorist groups.

The remarkable thing is that Western governments would have you believe that the Syrian opposition is all about moderate, democracy-loving rebels. That's a deception. My guess is the shooter is Islamic Front.