New details have emerged surrounding the Colorado shooting suspect’s plan, following Friday’s massacre in an Aurora movie theatre.

James Holmes, the suspected shooter, mailed his notebook to a University of Colorado professor more than a week before the shootings during a midnight showing of “The Dark Knight Rises,” according to celebrity gossip website TMZ.

However, the notebook wasn’t discovered until Monday, three days after the shooting which killed 12 people and injured 58. Fox News reports it was full of details and drawings about how the shootings were going to take place.

Both police and the FBI said the notebook was sitting in the mail room of the University since July 12, eight days prior to the massacre. It was reportedly addressed to a professor psychiatrist who treated patients at the campus’ university psychiatry facility, but it’s unknown if the professor had any contact with the shooter.

The notebook was discovered after another suspicious package was delivered to the university earlier this week. That package turned out to be nothing.

Earlier this year, Holmes dropped out of the same university’s neuroscience doctoral program, where he had studied mental health issues.

Meanwhile, Holmes former teachers and classmates are still trying to come to terms with his arrest.

“He excelled in academics, he was at the top of the class, and even back then he was ahead of every student,” said a male student.

“He was a clean-cut kid, he was well-dressed, he was articulate, he was a top, top student, he caused no trouble,” said a teacher who taught Holmes over 10 years ago.

“As a teacher, you’re thinking ‘this is one of my kids’ and then you also think ‘could I have done anything?’ or ‘did I see anything? Did I miss anything?’”

Holmes is expected to be formally charged on July 30.

The Denver Post reports background checks for people wanting to purchase firearms in Colorado have jumped more than 41 per cent since last Friday’s attack.