tbh, the argument is pointless. the problem is as follows
Information control : both sides have engaged in active information control and want to paint their own sides as good, so as to garner international sympathy and public opinion in their favor. sadly, both of them are in the wrong, and as such in a proxy war between super powers, the people of syria are dying.
Both USA and Russia are not without prior guilt : Both these countries are not without prior guilt, as evidenced in past conflicts globally, whether covert or overt. So, if its Russia this time, then it was USA before, and possibly in the future.
All sides are trying to advance their own agenda : The problem is not humanitarian or sectarian or theologic. The problem is of two global powers asserting their own agenda(or trying) and then failing to one up each other. All these so called "sources" paint a picture that is designed to raise the sympathy levels of their own side, and antagonize the public towards the other.
State actors, media, and journalism : Unfortunately it is very difficult to truly find independent journalists because most of these machines are propaganda for either side. While there might be truth , to an extent, to some of it, it is being paid for and modified by one or the other side for convenience. So there is no white or black, just grey. relax.