Holmes allegedly killed 12 people and wounded 58 others during the bloody rampage.
Prosecutors outlined their case against the suspect Monday, with survivors and family members of the victims present in the courtroom. Holmes is charged with more than 160 counts, including multiple counts of murder and attempted murder.
During the opening of the hearing, two Aurora police officers took the stand and described what they witnessed on July 20, 2012.
The officers said the suspected gunman was unusually "relaxed" on the day of the massacre. Having spotted Holmes next to his car behind the theater, Officer Jason Obiatt initially thought he was a fellow officer. Obiatt said he soon realized Holmes was the suspect when he didn't have normal emotional reactions.
"He seemed very detached from it all," Obiatt said, who then pointed his gun at Holmes and handcuffed him.
Obiatt proceeded to search Holmes and found an ammunition round in his pocket, two knives and a semi-automatic handgun on top of Holmes' car.
After the officer and his partner Officer Aaron Blue put Holmes in a patrol car, the suspect continued to fidget which led the officers to re-search him. Holmes was dressed in clad armor which worried officers who thought he may have easily hidden something in his bulky outfit.
During the arrest, the former neuroscience graduate student also volunteered that he had four guns and that there were "improvised explosive devices in his apartment."
According to authorities, Holmes entered the theater with a ticket and propped open a door before slipping out and returning with weapons and gas canisters.
The hearing at the Arapahoe County District Court in Centennial, Colo., is expected to take all week. Prosecutors say they plan to present potentially gruesome photos and videos in addition to 911 calls made following the massacre.
Legal analysts say the hearing could set the stage for a negotiated plea agreement by giving each side a better understanding of the other's case.
The Aurora police lead detective, first responders, the coroner, and a computer forensic specialist are set to give prosecutors' witness reports.
The hearing is the first extensive public disclosure of the evidence against Holmes. Court documents have been under seal following the shooting due to a court-imposed gag order.
Despite the gruesome information disclosed, MaryEllen Hanson, a relative to a 6-year-old victim killed in the shooting, says she hopes that a "first-hand-experience" of what happened can provide closure.
"It's one of those things that you almost have to face the devil," Hanson told ABC News. "I don't feel he has the right to intimidate people. I think it's really important to know the details."
In chilling information released to the public during Monday's court hearing, the suspect reportedly tried to call his university psychiatrist nine minutes before the killing began.
It is uncertain whether Holmes' attorneys plan to employ an insanity plea. His defense team has previously told Judge Sylvester that they believe Holmes is mentally ill.
After this week's delegations, Judge William Sylvester will decide whether the evidence is sufficient to put Holmes on trial.
ABC News and The Associated Press contributed to this report.
