James Holmes notebook
This is one of the pages in James Holmes' notebook showing a schematic for the Aurora theaterColorado Judicial Department

Jurors were presented with a chilling debate about how to kill innocent people in a notebook kept by former university student James Holmes, who's charged with murdering 12 people at a Colorado cinema.

The defence claimed the musings were proof Holmes was insane. The prosecution said it was clear evidence Homes was clear-headed and calculating.

No one denies that Holmes opened fire with an assault rifle in a midnight showing of a Batman movie at the Aurora cinema three years ago. But his defence team is arguing that he is not guilty of murder because he was compelled to kill by his schizophrenia.

In Holmes's notebook quest for the best way to kill lots of people, he wrote that biological weapons required too much know-how, serial killing resulted in too much contact with victims, and bombs were "too hard to build". He finally opted in the notebook for "mass murder/spree" ... but then wondered: "Airport or movie theater?"

'The cruel twists of fate are unkind to the misfortunate'

He drew schematics for his chosen cinema in the notebook and drew a plan, jotting: "Target random. The cruel twists of fate are unkind to the misfortunate." Holmes mailed the notebook to his psychiatrist at the University of Colorado just before the massacre.

A graduate student in neuroscience, Holmes also wrote that he believed he was mad, reports the Denver Post. He listed 13 ailments including schizophrenia and "borderline, narcissistic, anxious, avoidant and obsessive compulsive personality disorder," adding: "So, anyways, that's my mind. It's broken. I tried to fix it."

Despite the apparent rantings, a state-appointed testified that Holmes was sane during the attack. "Whatever he suffered from, it did not prevent him from forming intent and knowing the consequences of what he was doing," Dr. William Reid testified.

Jurors for the first time heard psychiatric interviews with Holmes in which he expressed regret about the shootings, reports ABC News.