The jury deliberated for less than three hours, starting Thursday after Holmes' parents made an emotional plea to spare their son's life because he is mentally ill. A court spokesman said the decision will be announced at 12:30 p.m. MDT.
The nine women and three men were asked to decide whether circumstances such as Holmes' mental illness, trouble-free childhood and lack of a prior criminal history reduce his "moral culpability" enough to justify sentencing him to life in prison without parole instead of death.
The same jury rejected Holmes' insanity defense, convicting him of murdering 12 people and trying to kill 70 others in the July 2012 theater attack. Colorado law defines insanity as the inability to know right from wrong.
During the sentencing phase, the defense called a court-appointed psychiatrist who previously testified for the prosecution that Holmes knew the difference between right and wrong and was therefore legally sane. But Dr. Jeffrey Metzner also said severe mental illness and delusions drove Holmes to kill, rather than hatred or a desire for notoriety.
"Having psychosis doesn't take away your capacity to make choices. It may increase your capacity to make bad choices," said Metzner, who diagnosed Holmes with schizoaffective disorder.
The defense also presented testimony from Holmes' friends from childhood through college, former neighbors and teachers and showed photographs and videos of Holmes as a baby and a smiling young boy. Holmes was a promising student working toward his Ph.D. in neuroscience at the University of Colorado before illness overtook his mind, his attorneys said.
Prosecutors said none of that outweighs the heinous nature of Holmes' planned and calculated shooting during a crowded midnight showing of a Batman movie in suburban Denver. They said he wanted to kill all of the more than 400 people who filled the auditorium and stopped at 12 because his assault rifle jammed.
They contended the violence was Holmes' attempt to assuage his failures in graduate school and romance.