The US media report that the accused in the Colorado shootings sent writings about shooting people to his university.
University of Colorado Denver confirmed it had received a suspicious package on Monday that it gave to the authorities, but they did not identify the sender.
US news outlets reported the suspect, neuroscience drop-out James Holmes, mailed writings that included crude drawings of people being shot.
The reports emerged as the first funeral of the 12 victims was held.
Gordon Cowden, 51, was the oldest of those killed. His teenage children were also in the theatre during the shootings but emerged uninjured.
James Holmes, 24, is being held over the massacre, which happened at a midnight showing of the new Batman film in Aurora, near Denver, on Friday.