>> reporter: three years ago this month, james holmes opened fire in a packed movie theater killing 12 people and wounding 7 others. this week the jury begins deliberations after two months of testimony. 270 witnesses, most survivors -- >> i told him i loved him and i would take care of our baby if he didn't make it. >> reporter: -- or first responders. >> by the time we pulled into the hospital she stopped talking. she lost consciousness. >> reporter: defense attorneys admitted holmes carried out the attack but argue he was legally insane or didn't know the difference between right and wrong. showing this video of him walking into a wall they said he should be found not guilty by reason of insanity and locked up into a mental institution. >> i do not believe if he were not mentally ill, this would have ever happened. >> reporter: the burden is on the prosecution to prove that holmes was, in fact saying