The man accused of killing a dozen people at a midnight screening of the 'The Dark Knight Rises' sent a journal detailing the rampage to a University of Colorado psychiatrist prior to the attack, only for it to go untouched in a campus mailroom, according to a Fox News report.

The diary of 24-year-old James Holmes -- "full of details about how he was going to kill people" -- was discovered Monday by authorities investigating another package at the school's Anschutz medical campus in Aurora, a law enforcement official told the network. The source also said that the package had been in the mailroom since July 12.

UPDATE: Original reports that said the notebook lay unopened for days before the attack may be inaccurate. The Denver Post reports that Holmes sent the package to his therapist on Friday -- the day of the shooting -- and that it arrived in the mailroom on Monday.

The notebook, intended for a psychiatrist who also teaches at the university, reveals haunting sketches with stick-figure assailants carrying out the attack.

“There were drawings of what he was going to do in it -- drawings and illustrations of the massacre," police told Fox News.

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  • James E. Holmes

    James E. Holmes, left, appears in Arapahoe County District Court, with defense attorney Tamara Brady, right, Monday, July 23, 2012, in Centennial, Colo. Holmes is being held on suspicion of first-degree murder, and could also face additional counts of aggravated assault and weapons violations stemming from a mass shooting on Friday, July 20, in a movie theater in Aurora, Colo., that killed 12 and injured dozens of others. (AP Photo/Denver Post, RJ Sangosti, Pool)

  • James E. Holmes, Tamara Brady

    People in the courtroom listen to the court hearing of James E. Holmes in Arapahoe County District Court Monday, July 23, 2012, in Centennial, Colo. Holmes is accused of killing 12 and wounding 58 in a shooting rampage in a Colorado theater on Friday, July 20. (AP Photo/Denver Post, RJ Sangosti, Pool)

  • James E. Holmes

    James E. Holmes appears in Arapahoe County District Court, Monday, July 23, 2012, in Centennial, Colo. Holmes is being held on suspicion of first-degree murder, and could also face additional counts of aggravated assault and weapons violations stemming from a mass shooting last Friday in a movie theater in Aurora, Colo., that killed 12 and injured dozens of others. (AP Photo/Denver Post, RJ Sangosti, Pool)

  • In this image taken from video provided by KUSA.com, James Holmes, left, the suspected gunman in Friday's Colorado theater massacre, makes his first appearance in court with his attorney Tamara Brady in Centennial, Colo. on Monday, July 23, 2012. (AP Photo/KUSA.com)

  • Carol Chambers

    Carol Chambers, district attorney for the 18th Judicial District, speaks during a media availability after a court appearance by James Holmes at the Arapahoe County Courthouse, Monday, July 23, 2012, in Centennial, Colo. Twelve people were killed and dozens were injured in a shooting attack early Friday at a packed theater during a showing of the Batman movie, "The Dark Knight Rises." Police have identified the suspected shooter as Holmes, 24. (AP Photo/Alex Brandon)

  • James E. Holmes, Tamara Brady

    James E. Holmes, center, appears in Arapahoe County District Court, with public defenders Tamara Brady, right, and Daniel King Monday, July 23, 2012, in Centennial, Colo. Holmes is accused of killing 12 and wounding 58 in a shooting rampage in a movie theater on Friday, July 20 in Aurora, Colo. (AP Photo/Denver Post, RJ Sangosti, Pool)

  • James E. Holmes

    James E. Holmes appears in Arapahoe County District Court, Monday, July 23, 2012, in Centennial, Colo. Holmes is being held on suspicion of first-degree murder, and could also face additional counts of aggravated assault and weapons violations stemming from a mass shooting Friday, July 20, in a movie theater in Aurora, Colo., that killed 12 and injured dozens of others. (AP Photo/Denver Post, RJ Sangosti, Pool)

  • David Sanchez

    David Sanchez, whose son-in-law was critically wounded, speaks after a court appearance by shooting suspect James Holmes at the Arapahoe County Courthouse, Monday, July 23, 2012, in Centennial, Colo. Twelve people were killed and dozens were injured in the shooting attack early Friday at an Aurora, Colo., theater during a showing of the Batman movie, "The Dark Knight Rises." (AP Photo/Alex Brandon)

  • Family members of a victim from last week's theater shooting in Aurora, Colo., link hands as they arrive for a court appearance by shooting suspect James Holmes at the Arapahoe County Courthouse, Monday, July 23, 2012, in Centennial, Colo. Twelve people were killed and dozens were injured in the shooting attack early Friday at the packed theater during a showing of the Batman movie, "The Dark Knight Rises." (AP Photo/Alex Brandon)

  • A woman, third from left, is led to the courtroom where James Holmes appears in Arapahoe County District Court, Monday, July 23, 2012, in Centennial, Colo. Holmes is the suspect in the mass shooting last Friday in a movie theater in Aurora, Colo., that killed 12 and injured dozens of others. (AP Photo/Barry Gutierrez)

  • Anggiat Situmeang,

    Anggiat Situmeang, center, who suffered an injury in last week's theater shooting in Aurora, Colo., is helped inside to see a court appearance by alleged shooter James Holmes, at the Arapahoe County Courthouse Monday, July 23, 2012, in Centennial, Colo. (AP Photo/Alex Brandon)

  • James E. Holmes

    Assistant District attorney Karen Pearson speaks at a hearing for James E. Holmes in Arapahoe County District Court, Monday, July 23, 2012, in Centennial, Colo. Holmes is being held on suspicion of first-degree murder, and could also face additional counts of aggravated assault and weapons violations stemming from a mass shooting last Friday in a movie theater in Aurora, Colo., that killed 12 and injured dozens of others. (AP Photo/Denver Post, RJ Sangosti, Pool)

  • James E. Holmes

    James E. Holmes appears in Arapahoe County District Court, Monday, July 23, 2012, in Centennial, Colo. Holmes is being held on suspicion of first-degree murder, and could also face additional counts of aggravated assault and weapons violations stemming from a mass shooting last Friday in a movie theater in Aurora, Colo., that killed 12 and injured dozens of others. (AP Photo/Denver Post, RJ Sangosti, Pool)

  • James E. Holmes

    James E. Holmes appears in Arapahoe County District Court, Monday, July 23, 2012, in Centennial, Colo. Holmes is being held on suspicion of first-degree murder, and could also face additional counts of aggravated assault and weapons violations stemming from a mass shooting last Friday in a movie theater in Aurora, Colo., that killed 12 and injured dozens of others. (AP Photo/Denver Post, RJ Sangosti, Pool)

  • James E. Holmes

    James E. Holmes, left, appears in Arapahoe County District Court, with defense attorney Tamara Brady, right, Monday, July 23, 2012, in Centennial, Colo. Holmes is being held on suspicion of first-degree murder, and could also face additional counts of aggravated assault and weapons violations stemming from a mass shooting on Friday, July 20, in a movie theater in Aurora, Colo., that killed 12 and injured dozens of others. (AP Photo/Denver Post, RJ Sangosti, Pool)

  • James E. Holmes

    District Court Judge William Blair Sylvester speaks as James E. Holmes appears in Arapahoe County District Court, Monday, July 23, 2012, in Centennial, Colo. Holmes is being held on suspicion of first-degree murder, and could also face additional counts of aggravated assault and weapons violations stemming from a mass shooting last Friday in a movie theater in Aurora, Colo., that killed 12 and injured dozens of others. (AP Photo/Denver Post, RJ Sangosti, Pool)

Holmes is accused of killing 12 people and injuring 58 others during a Friday showing of the new Batman film at the Century 16 Theater in Aurora.

Calls and emails made by The Huffington Post to the University of Colorado were not immediately returned.

On Monday, Holmes made his first court appearance following the massacre. The suspect appeared dazed and sleepy during the brief hearing, frequently closing his eyes during the proceedings.

Holmes is now behind bars at the Arapahoe County Detention Center, where he has reportedly spat on jail guards and requested a summary of how the film ends.

Holmes will face formal charges from prosecutors on July 30.