James Holmes, who killed 12 and injured dozens of others when he went on a shooting rampage at a packed screening of "The Dark Knight Rises" premiere, reportedly sent a notebook packed with details on how he will kill people to a psychiatrist at the University of Colorado.

The chilling notebook was sent prior to the deadly attack in Aurora, Colorado, and the mail remained unopened for up to a week before it was finally found and revealed on Monday, three days after the shootings.

A suspicious package sent from James Holmes was found at the campus, and FBI agents and police officers were called to investigate. The package was not dangerous. However, during their thorough investigation of the campus' mail room, they discovered an unopened package sent from Holmes, addressed to the school's psychiatrist.

A source told Fox: "Inside the package was a notebook full of details about how he was going to kill people. There were drawings of what he was going to do in it - drawings and illustrations of the massacre."

If the notebook is packed with the details as it claims to be, then it proves the belief that the attack had been meticulously planned and premeditated.

The 24-year-old suspect who carried out the atrocious attack at the Century 16 movie theater, was a medical school dropout and was studying for a neuroscience PhD at the University of Colorado School of Medicine. It has been revealed that he only just dropped out last month and had been studying right up until June.

Holmes is described as a loner, a recluse, who kept to himself. One student commented that no one knew him. It has been reported that he left music on in his apartment, blaring, just moments before carrying out the massacre.

James Holmes is a local resident of the community who only lived a few miles away from the theater. Witnesses say he wore a bulletproof vest and mask as he opened fire with two pistols and a shotgun at the Century 16 Movie Theaters at the midnight showing of the latest Batman movie premiere. A motive for the shooting has not emerged yet and nothing in his background suggests why he would carry out such an evil act.