Prosecutors claim James Holmes told an unidentified University of Colorado classmate in March that he wanted to kill people, which was four months before the shootings.
The alleged conversation would have occurred at roughly the same time that police said Holmes began receiving "a high volume of deliveries" at his home and at the university. Police haven't revealed what those packages contained, but they said he ordered thousands of rounds of ammunition on the Internet.
The court document was filed after Holmes' defense team tried to quash prosecutors' request for his educational records. Prosecutors argued that the documents are relevant to the investigation of the crime. The judge has not decided whether the school records will be used as evidence.
Prosecutors also hope to use a notebook as evidence in the case. The notebook was part of a package Holmes sent to his university psychiatrist, Lynne Fenton. She is expected to testify at an Aug. 30 hearing.
ABC News and the Associated Press contributed to this report.