The suspect in the Colorado cinema massacre posted a notebook "full of details about how he was going to kill people" to a psychiatrist, it has been reported.
The advance warning of the mass killing - which was sent to the member of staff at the University of Colorado - lay unopened in a post room for as long as a week before its discovery on Monday, a police source told FoxNews.com.
It is claimed FBI agents were called to the university's medical campus in Aurora on Monday morning after the psychiatrist, who is also a professor at the school, reported receiving a package believed to be from the suspect, James Holmes.
It turned out to be from someone else, but a search of the post room uncovered another package sent to the psychiatrist with Holmes' name in the return address, the broadcaster reported.
The authorities got a warrant from a county judge and took the package away on Monday night, a second police source said.
"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," according to the unnamed source.
The source said the package had been in the mailroom since July 12, though another source who confirmed the discovery could not say if the package arrived prior to Friday's massacre.
Both sources said the intended recipient of Holmes' notebook was a professor who also treated patients at the psychiatry outpatient facility where the first suspicious package was delivered. It was not clear why it had not been delivered to the psychiatrist.
FBI agent Dave Joly declined to comment on the claims, citing a gag order issued Monday by Arapahoe County District Judge William Sylvester.
Holmes appeared in court for the first time on Monday. He did not speak during the 10-minute hearing, and appeared dazed.
He had refused to co-operate with law enforcement officers ahead of the hearing at the Arapahoe County Justice Centre, police sources say.