Reasons for starting wars:
Let us see,
Vietnam - Golf of Tonkin - made up
Iraq - WMD - made up
Afghanistan - 9/11 - not Afghanistan, still seeking true culprits
Libya - made up
Syria - made up
Assad is winning, ISIS is being wiped out, it would be ludicrous to suggest Assad would carry out such an attack considering the repercussions.
The Syrian Free Army or ISIS if you like have everything to gain by faking an attack.
Let's see how our 'bought and paid for' media react if such an attack does take place.