Prosecutors who displayed the pictures at a hearing that ended Wednesday argued the photos display "identity, deliberation and extreme indifference."
Holmes' attorneys - who have been setting up an insanity defense and said they might present testimony about the defendant's mental health - decided not to call any witnesses.
A judge is due to rule by Friday whether prosecutors presented enough evidence to justify Holmes standing trial for more than 160 felony counts stemming from the July 20 attack, which killed 12 people and injured 70. Holmes, 25, may enter a formal plea that day.
The three-day hearing occurred as the nation still recovers from the shock of last month's shooting at a Connecticut elementary school that killed 20 children and six adults. It wrapped up just as the Colorado Legislature began its session and pledged to tackle gun violence, and Vice President Joe Biden met with families of victims as part of the White House's own gun control push.
Prosecutors presented the most detailed description of the attack and Holmes' alleged months of preparation. But they never addressed the mystery of why Holmes opened fire six weeks after leaving a neuroscience graduate program.
Legal experts say evidence against Holmes is so strong that the case may end in a plea deal. That would make the hearing the only detailed presentation of the evidence that victims, their families and the public will hear.
Holmes sat impassively through much of the proceedings, watching intently as a surveillance video showed him entering the theater lobby. Family members, who had a better view of Holmes' face than the media did in the packed courtroom, said he smiled multiple times, especially when the photos were shown.
"He's not crazy, he's evil," said Tom Teves, whose 24-year-old son Alex was killed in the attack. "He's an animal."
Prosecutor Karen Pearson argued that Holmes meticulously planned the attack, starting with the online purchase of two tear gas canisters on May 10, followed by buying online 6,295 rounds of ammunition, and body armor, as well as going to local sporting goods stores to purchase an assault rifle, shotgun and two Glock pistols. He bought his ticket for opening night of "The Dark Knight Returns" nearly two weeks before the attack and visited the theater early, photographing the layout.
He rigged an elaborate booby-trap system in his apartment with three different triggers, hoping the detonation would distract police from the carnage he planned a few miles away, investigators testified. The trap was never sprung.
About six hours before the attack, Holmes took a series of photos on his phone. In one he wears black contact lenses and a black stocking cap, with two tufts of his dyed-red hair sticking out like a pair of horns. In another he holds a pistol beneath his face, twisted into a grin. In a third, much of his arsenal - the assault rifle and shotgun, magazines for ammunition, tactical gear and bags to carry rounds - is displayed on a red sheet on his bed.
When Holmes burst into the theater and opened fire just after midnight July 20 there were as many as 1,500 people crowded into the seats and in the auditorium next door, prosecutors said. Some of Holmes' bullets pierced the wall and injured people in the adjacent theater. Holmes fired about 70 rounds, many of which apparently hit multiple people, and was only prevented from shooting more because his rifle jammed, prosecutors said.
"He didn't care who he killed or how many he killed, because he wanted to kill all of them," Pearson said Wednesday.
The hearing is a legal formality to establish the prosecution's case. Defense attorneys rarely mount a full-blown case during such hearings, preferring to save their witnesses for the trial. Defense attorney Tamara Brady offered a limited, but notable, preview when she questioned an ATF agent who had listed Holmes' extensive online purchases.
Brady asked whether any Colorado law prevented "a severely mentally ill person" from buying the ammunition, body armor and handcuffs that Holmes purchased online. The answer: No.
Holmes had seen a psychiatrist at the University of Colorado, Denver. There was no testimony about his year at the school during the hearing. He left the neuroscience graduate program after failing a key exam.
If Holmes is found sane, goes to trial and is convicted, his attorneys can try to stave off a possible death penalty by arguing he is mentally ill. Prosecutors have yet to say whether they will seek the death penalty. They will have 90 days from Holmes' arraignment to hold Holmes for trial to decide.
If Holmes is found not guilty by reason of insanity, he would likely be sent to the state mental hospital, not prison. Such a defendant is deemed not guilty because he didn't know right from wrong and is therefore "absolved" of the crime, said former Jefferson County District Attorney Scott Storey. His case would be reviewed every six months until he's deemed sane and released.
Last year, Bruco Strong Eagle Eastwood was acquitted by reason of insanity of attempted first-degree murder in the wounding of two eighth-graders outside a school not far from Columbine High School. Eastwood is spending time in a mental hospital.
Associated Press writers Thomas Peipert, Nicholas Riccardi and Colleen Slevin contributed to this report.