The former neuroscience graduate student accused of killing 12 people in the Colorado movie theatre shooting sent a package to his university before the attack describing a violent assault, multiple news outlets reported Wednesday.

Citing unnamed law enforcement sources, the Fox News website reported that shooting suspect James Holmes sent a notebook to the University of Colorado, Denver.

Fox said the notebook contained drawings of stick figures being shot and a written description of an upcoming attack. The package containing it was addressed to a psychiatrist at the school, the website reported.

It was unclear if Holmes, 24, had had any previous contact with the person. The neuroscience program that he withdrew from on June 10 included professors of psychiatry.

Holmes is accused of opening fire on a theatre showing the new Batman movie, killing 12 people and injuring 58. He is due to hear the charges against him at a court hearing scheduled Monday.

James Holmes (left) sits with public defender Tamara Brady during his first court appearance in Aurora, Colo., on Monday. (RJ Sangosti/Reuters)

NBC News, also citing unnamed sources, reported that Holmes told investigators to look for the package and that it described killing people.

The FBI and other law enforcement agencies refused to confirm the reports to The Associated Press.

The University of Colorado, Denver, issued a statement saying it could not confirm the reports or discuss any aspects of the investigation, citing a gag order placed on the case by a judge. It said that packages to the main mailroom of the Anschutz Medical Campus, where Holmes studied, are not tracked unless the U.S. Postal Service requires a signature upon delivery.

Before the gag order was issued, police said Holmes received more than 50 packages at the school and his home that apparently contained ammunition, combat gear and explosive materials that he used in the attack and to booby trap his Aurora apartment.

Holmes's apartment building remained closed on Wednesday, although his defence team stopped by for a brief visit. They left without answering reporters' questions.

Holmes was allegedly stockpiling for the attack while he studied at the school's neuroscience program. He bought a shotgun and pistol in May, authorities say. On June 7, the date he took a year-end oral exam, he bought an assault rifle. He filed paperwork to leave the program three days later and did not provide a reason, the university has said.

On June 25, he filed an application to join a private gun range in eastern Colorado, but the club's owner, hearing what he described as a "bizarre" outgoing voice mail on Holmes' cellphone recorded in a low voice with heavy-breathing, told his staff to watch out for the man. Holmes never came to the range.