CENTENNIAL, Colo. (CBS4)– A key piece of evidence in the Aurora theater shooting trial is set to be introduced. The notebook belonging to the gunman who opened fire in a crowded theater will be presented in court on Tuesday.

James Holmes kept a notebook that he sent to his psychiatrist which was received after the July 20, 2012 shooting. He has pleaded not guilty by reason of insanity for killing 12 people and leaving dozens of others injured.

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The notebook reportedly contains plans for the theater shooting. Prosecutors believe it will give jurors a valuable insight into Holmes’ mental state before the shooting.

James Holmes with this defense team in court (credit: CBS)

James Holmes with this defense team in court (credit: CBS)

The notebook was received at the University of Colorado Anschutz Medical Center where Holmes had been studying in the neuroscience program until he withdrew. It was sent to Dr. Lynne Fenton, a psychiatrist he had been seeing.

The notebook turned up after the attack and bomb experts, including Denzel Lukens from Adams County, were called to examine the package.

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“I could see some burned edges inside the book and currency slipping out that you could see was burned around the edge,” said Lukens during testimony in court.

News reports indicated the notebook contained Holmes’ writing before the attack and violent images.

Among those in the theater that night was Brooke Cowden, who was 16 years old at the time. Her father, Gordon Cowden, was shot.

“I was still lying on the ground while I was expecting either the gas or a bullet, my attention turned to my dad saying, ‘I love you,'” said Brooke.

She said when there was a pause in the firing she was able to escape but in her words, had to abandon her father.

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Another survivor, Jacqueline Fry, was at the movie with a group from a Red Robin restaurant. As she testified on Tuesday, she struggled to tell the story of how she was shot multiple times and her friend, Alex Sullivan, was killed.