The source, whose name was not reported, told the newspaper, Holmes told his psychiatrist, Lynne Fenton, he fantasized about killing "a lot of people." Six weeks later, on July 20th, he allegedly shot and killed 12 people and injured 58 others at an Aurora, Colo., midnight screening of a Batman movie, "The Dark Knight Rises."
Holmes, 24, is charged with 166 counts of murder, attempted murder and other charges.
Fenton notified CU police about Holmes' statement, but when asked if she wanted to put him on 72-hour psychiatric hold, she refused, the Post reported Wednesday.
Meanwhile, the university released nearly 3,800 emails from the school's email system that mention Holmes by name or that were sent to or from his email accounts. The school said it withheld any emails referencing his mental health, the crime or any personal communication involving Holmes.
Most of the messages are mundane, the Post said, though some do reference the shooting rampage.
One professor in the computation bioscience program sent a message mentioning Holmes' romantic relationship with a fellow graduate student.
"She, fortunately, it turns out is in India right now," the email said. "She knows, and is pretty freaked out."
Holmes is currently being held without bond at the Arapahoe County Jail. He is scheduled to appear in court next week, the Post said.