Arapahoe County District Attorney George Brauchler said his office consulted with numerous victims before deciding to seek the death penalty for Holmes, who appeared to have no reaction to the announcement, The Denver Post reported.
"For James Eagen Holmes, justice is death," Brauchler said.
Holmes is charged with 166 counts of murder, attempted murder and other offenses in the July 20, 2012, theater massacre in Aurora. Fifty-eight other people were wounded.
He is scheduled to go on trial Aug. 5.
Last week his attorneys disclosed in a court filing Holmes offered to plead guilty in exchange for a sentence of life without parole. Prosecutors said Holmes failed to meet their requirements for a deal.
In their filing, Holmes' attorneys said they may pursue a mental-health defense and file numerous pre-trial motions if the case goes to trial, the Post reported.
"The issue is not whether they're going to enter an insanity plea on his behalf," said Dr. Steven Pitt, a forensic psychiatrist. "I suspect the issue is more about the exposure that ... places on their client."
Holmes' attorneys shied away from entering an insanity plea last month.
Pitt said the defense may have hesitated because such a plea is extremely risky.
"When you're entering an insanity plea, you're saying 'I did it,' " Pitt said. "'I did it but I wasn't in my right mind when I committed the offenses, and I couldn't appreciate the wrongfulness of my conduct.'"
Attorneys not affiliated with the case said Holmes' lawyers likely will attempt all they can to achieve their main goal in the case.
"In any potential death-penalty case," Denver attorney Karen Steinhauser, a former prosecutor, told the Post, "the primary goal of the defense attorneys is to save their client's life."