james holmes was once a doctoral student and neuroscientist-in-training .
but prosecutors say in the months before the shooting he was preparing for violence , amassing weapons and sending threatening text messages .
said holmes searched online for ` rational insanity ' knew exactly what he was doing when he opened fire at the 2012 batman premiere .
if the jury finds holmes was mentally ill at the time of the shooting , he will avoid jail and be committed indefinitely to a state psychiatric hospital .