James Holmes penned the disturbing details of the planned massacre in a journal, which he mailed to University of Colorado professor more than a week before the he carried out the actions at the Aurora movie theatre.
According to TMZ, FBI and police found the journal while they searched a mailroom on the campus – also in Aurora – on Monday.
Reportedly, the notebook was sitting in the facility unopened since it was mailed on July 12, which is eight days before the shooting.
The package containing the documented evidence was sent from the mastermind himself, Holmes, and according to a FOXNews.com source: “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."
The source went on to say the sketches included gun-operating stick figures.
The package containing the time-sensitive parcel was reportedly address to a professor and psychiatrist who treated patients at the University of Colorado psychiatry facility.
It’s undetermined if the professor ever had communication with Holmes.
‘PHOTOS’ Click through to see the aftermath in Aurora, Colorado