There is no window into the soul of evil.
You can't see empty. You do feel it, which is the aim of cruel and senseless intentions. The content is discernible and disturbing: blood and bodies. The props are simple: guns and grenades. The desired effect is easily achieved: anxiety, anger, and deep-set fear.
Violence of the ilk perpetrated in Paris shakes us, literally. It is revelatory of a new and emerging world order that shouldn't surprise us; its reverberations, after all, are neither new nor infrequent.
Rational folks will want answers. There are no easy ones.