prosecutors said james holmes , 27 , was once a sought-after neuroscientist-in-training , but evidence shows that months before the shooting he was preparing for violence .
the prosecution is trying to prove that holmes was not mentally ill and knew exactly what he was doing the night of july 20 , 2012 , when he opened fire during the midnight premiere of the batman film ` the dark knight rises ' .
if not , prosecutors will press for the death penalty over life in prison without parole .