The disclosure came in court documents filed by lawyers for James Holmes, 24, who is accused of opening fire last Friday on a packed showing of the latest Batman movie, "The Dark Knight Rises," in the Denver suburb of Aurora.
The defence attorneys, in their request to an Arapahoe County district judge, are seeking a court order requiring prosecutors to turn over the contents of a package that Holmes sent to Dr. Lynne Fenton and was later seized by investigators.
"Mr Holmes was a psychiatric patient of Dr Fenton, and his communications with her are protected," the filing said.
Fenton, medical director for student mental health services at the University of Colorado-Denver Anschutz Medical Campus, provides medication and psychotherapy for graduate students in addition to her teaching responsibilities, according to a school website.
A professional biography of Fenton posted on the site said she had conducted research on schizophrenia, including a two-year grant to work in the schizophrenia research department of the U.S. Department of Veterans Affairs from 2008 to 2010.
Fenton is also a member of the campus-based "behavioral assessment and threat assessment team," which helps faculty and staff deal with "individuals who may be threatening, disruptive or otherwise problematic," according to that group's website.
It could not be ascertained if Fenton was caring for Holmes under the threat-assessment program or under routine counseling she provided to students on campus.
Fenton could not immediately be reached by Reuters for comment, and a spokeswoman for the University of Colorado medical school declined comment, citing restrictions under a gag order issued by the judge presiding over the case.
The university, where Holmes had been enrolled as a doctoral student of neuroscience, confirmed earlier this week that a suspicious package was delivered by mail on Monday and that it was "immediately investigated and handed over to authorities within hours."
Fox News has reported, citing an unnamed law enforcement source close to the investigation, that two packages were sent by Holmes to a psychiatrist on the faculty of the University of Colorado, and that one contained a notebook detailing the shooting scenario. According to Fox News, the notebook contained hand-drawn illustrations of stick figures shooting at other stick figures.
The defence motion accuses of the government of leaking information to the media in defiance of a gag order, thereby jeopardizing Holmes' rights to due process and fair trial by an impartial jury. It says his lawyers will request a hearing to determine "appropriate sanctions for this misconduct."
Prosecutors, responding to the discovery motion, disputed various elements of media accounts as being erroneous, suggesting that anyone who had provided information to Fox News and other outlets lacked real knowledge of the case.
"These factual errors lead (the government) to believe ... that the media is getting information from hoaxers, fraudsters, or maybe from nobody at all by creating fake 'law enforcement sources' out of whole cloth," prosecutors said in their filing.
Formal charges against the suspect, who dyed his hair bright orange and was said by authorities to have referred to himself as the Joker - Batman's comic book arch enemy - are expected to be filed in court on Monday.
The judge in the case, William Sylvester, set a hearing on the defence discovery motion to be held as part of Monday's proceedings.
Arrested within minutes of the shooting rampage at his car in the theater's parking lot, Holmes is being held in solitary confinement in the local jail.
In addition to charges stemming from one of the worst outbursts of U.S. gun violence in recent years, he is accused of wiring his apartment with enough explosives to have leveled the entire building if they had been detonated.
The apartment house was evacuated when the booby traps were discovered. But the explosives were later safely dismantled and removed by authorities, and Holmes' neighbors began returning to their homes on Wednesday night.
The latest disclosures about the suspect came to light as mourners attended the third funeral in as many days for one of the victims of the shooting rampage, this one for an 18-year-old high school graduate, Alexander J. "AJ" Boik," who was bound for art college in the fall.
Aurora's Queen of Peace Catholic Church was filled with hundreds of mourners, including Colorado Governor John Hickenlooper, Aurora Mayor Steve Hogan and a contingent of Aurora police officers and firefighters.
Boik was one of the youngest among 12 people, aged 6 to 51, killed in the hail of gunfire early last Friday, just after midnight. Of the 58 wounded, 12 remain hospitalized, including five in critical condition.
