The suspect in the Colorado cinema shooting tried unsuccessfully to call his university psychiatrist nine minutes before he opened fire during a Batman movie premiere, a court heard on Thursday.
James Holmes made the call to an after-hours number at a hospital at the University of Colorado, defence lawyer Tamara Brady said.
The number would have allowed him to reach psychiatrist Lynne Fenton, but she was not available and it was unclear why he attempted to contact her, the court heard.
Holmes, 24, is accused of the July 20 shooting that left 12 people dead and 58 wounded.
The detail about the phone call came out during a hearing about Holmes' relationship with Ms Fenton, to whom he sent a package containing a notebook that reportedly contained violent descriptions of an attack.
Prosecutors are asking a judge to allow them to review the notebook as part of their investigation, but defence lawyers say the journal is protected by doctor-patient privacy laws, and is inadmissible.
Ms Fenton was unaware Holmes had tried to contact her and testified that she met him only once, on June 11.
She told the court she thought their privileged relationship was limited to that day.