what makes their eyes go dead?

you always hear how their eyes
were black holes
as they committed some
atrocity
like the man
who just stomped his
2 year old to death
killing him way past dead
last weekend in california
or the woman who
drove a knife repeatedly into
her aging father's back
or even my cousin
as he held his young wife's
shot gurgling body down
so it could bleed out
while family and cops
stood in horror
and we saw black holes
dead eyes in his face
he didn't even look like my cousin
some zombie stranger instead
just like the father killing his
baby son
people holler
people grab at them
they don't hear
their black eyes don't see
they just do what they do
as if possessed

where is the chemistry in this?
somebody tell me
there is an explaination
and don't tell me about the devil
tell me how
the 'normal' person
suddenly does these things?
the good neighbor
the good co-worker
the good child
don't tell me about the devil
but i do believe
their soul is gone
how did that happen?
what ate it up?
and can we make it stop doing that?