Whatever it is that sits locked away in a clerk’s office at the Arapahoe County courthouse could hold the key to understanding why a gunman opened fired at an Aurora movie theater, killing 12 and injuring 58.

In court filings, the judge, prosecutors and defense attorneys in the case involving suspect James Holmes have described the item as a “package.” Multiple sources speaking anonymously to multiple news agencies have said it is a notebook, one in which Holmes may have detailed murderous plans before mailing it to his psychiatrist at the University of Colorado.

But is it evidence?

That question will dominate the next two scheduled court hearings for Holmes, the first of which is Thursday afternoon.

Holmes’ attorneys are arguing that prosecutors should not be able to view the package because, they have argued, it is a confidential communication between a doctor and a patient. Deciding whether they are right will require 18th Judicial District Chief Judge William Sylvester, who is handling Holmes’ case, to closely read the Colorado law that creates doctor-patient confidentiality.

“The big issues for the court to decide are whether or not a privileged relationship between psychiatrist and patient actually exists, whether anything the patient has done has waived that privilege and whether there is an exception,” said Patrick Furman, a law professor at the University of Colorado.

If Holmes’ attorneys can show that Holmes was a patient of the psychiatrist — Dr. Lynne Fenton — and that the package was mailed to her as part of the treatment relationship, then prosecutors will have a hard time being able to see it, said David Kaplan, the former head of the state public defender’s office.

“If that is established, then nobody gets to see it,” Kaplan said. “He (Holmes), as the holder of that privilege, looks up and says, ‘I don’t want to reveal it.’ “

But the package’s timing is important, Furman said. If it was mailed after Holmes stopped seeing Fenton as a patient — he left the school weeks before the shooting — prosecutors might argue that the doctor-patient relationship had ended. Holmes’ attorneys would probably counter that by saying that any additional communication with Fenton should remain confidential, Kaplan said.

Because Fenton apparently took concerns about Holmes to authorities, prosecutors might also argue that the package fits within a “dangerous patient exemption.”

“If there was a legal requirement that she report behavior, then privilege is limited and doesn’t cover certain topics,” Furman said. “But even if the court were to find a waiver because of that communication, … it does not mean it’s a waiver to all other communications.”

To make their arguments, prosecutors and defense attorneys will have to rely on documents and witness testimony. Prosecutors have signaled in case filings that they have subpoenaed witnesses for the Aug. 30 hearing at which the package is scheduled to be discussed.

The hearing Thursday will center on whether prosecutors should have access to roughly 100 pages of educational documents produced by CU. Holmes’ attorneys don’t want prosecutors to get the documents, which prosecutors say they need to prepare for the Aug. 30 hearing.

If prosecutors are denied access to the package now, that does not mean it will be off-limits forever. If Holmes raises a mental-health defense at trial, the doctor-patient privilege is waived, and prosecutors can see his medical and mental-health records, Kaplan said.

John Ingold: 303-954-1068, jingold@denverpost.com or twitter.com/john_ingold