CENTENNIAL, Colo. -- In a brown spiral notebook titled "Of Life," Colorado theatre shooter James Holmes scrawled a self-diagnosis of his "broken mind" and described his "obsession to kill" since childhood.

He made lists of weapons he planned to buy and included detailed drawings of the theatre complete with pros and cons of attacking different auditoriums.

He wrote that his decision to storm the crowded auditorium came after a "lifelong hatred of mankind," and that his failures in graduate school served as the catalyst but were not the cause of the violence.

"Most fools will mistake correlation for causation," Holmes wrote. "The message is there is no message."

However, he also revealed that the "causation is my state of mind for the last 15 years."

The notebook that was mailed to Holmes' psychiatrist before the attack offered the first glimpse into Holmes' mental state during the shooting. A gag order had previously kept those details secret.

Prosecutors have focused on portions of the notebook that detail Holmes' planning of the attack and say it is evidence that he was sane at the time of the shooting. The contention stands at the heart of the prosecution's case, which is also expected to include testimony from two court-appointed doctors that Holmes was sane when he opened fire on a packed midnight showing of a Batman movie.

However, defence attorney Daniel King said confusing musings about Holmes' life make up a greater part of the notebook. King cited ramblings by Holmes on the meaning of life and death, and the word "why" repeated over several pages.

Holmes has pleaded not guilty by reason of insanity in the attack that killed 12 people and wounded 70 on July 20, 2012.

While testifying. Aurora police Detective Sgt. Matthew Fyles read several passages from the notebook, including one in which Holmes detailed the "obsession to kill" since he was a child and how to carry it out.

Holmes dismissed biological warfare and serial murder as ways to act out his obsession and instead chose what he called a "mass murder/spree." He wrote that he considered attacking an airport but didn't want to be mistaken for a terrorist.

Holmes also wrote that he needed to research firearms along with the law and mental illness, Fyles testified.

Fyles said the notebook was mailed to Holmes' psychiatrist, Lynne Fenton, in a white bubble mailer with 16 stamps depicting scientists. The mailer contained twenty $20 bills, some of which were dispersed throughout the notebook, and the bills were all burned to some extent.

While cross-examining the detective, King said Holmes wrote that death is "life's fallback solution to all problems." In another section, Holmes said, "the real me is fighting the biological me."

Jurors were given copies of the notebook for several minutes to read themselves. They will have access to the writings again during deliberations.

The first month of Holmes' death penalty trial was dominated by dramatic and emotional accounts of survivors, technical testimony from investigators, and the recollections of Holmes' neuroscience professors and classmates, who said he never seemed detached from reality.

District Attorney George Brauchler has promised to show jurors days' worth of interviews with Holmes by psychiatrists William Reid and Jeffrey Metzner. Both doctors determined Holmes suffered mental illness but was sane at the time of the shootings.

Holmes' lawyers disagree, saying his mind was so distorted by schizophrenia that he could no longer tell right from wrong. They plan to call at least two doctors of their own who also interviewed Holmes and found he suffered a serious psychotic illness.

If jurors find Holmes not guilty by reason of insanity, he would be sent indefinitely to a state psychiatric hospital. Prosecutors are urging them to find Holmes guilty and sentence him to be executed.