On Monday, jurors will thoroughly examine those seven minutes in a trial that experts say could last months. The prosecution has said it will seek the death penalty. Holmes has pleaded not guilty by reason of insanity.
Jurors will also be asked to consider events that occurred before and after the July 20, 2012, shooting
-- namely, evidence that appears to show Holmes planned his attack, even going so far as to buy his movie ticket 12 days before, along with police allegations that officers who arrived to search Holmes' apartment had to navigate booby traps incorporating gasoline and grenades
According to police, Holmes attended the midnight showing of "The Dark Knight Rises" at the Century Aurora 16 Multiplex Theater but left through a rear door alongside the movie screen, propping it open behind him.
Holmes returned in "head-to-toe protective gear," including a gas mask, about 18 minutes into the movie, police said, and threw two tear gas canisters into the theater before opening fire with an AR-15 rifle, a 12-gauge shotgun and at least one .40-caliber handgun.
The attack killed 12 people
and wounded another 70, a level of violence not seen in Colorado since the Columbine High School shooting
Five days later, authorities discovered a package in a University of Colorado-Denver mail room that police say Holmes apparently sent.
Colorado authorities had no previous contact with Holmes, outside of a 2011 speeding summons, and he graduated in 2010 from the University of California, Riverside, with highest honors and a bachelor's degree in neuroscience. He enrolled as a doctoral candidate in the University of Colorado School of Medicine's neuroscience program in 2011 but dropped out the following year
without providing a reason, according to a university spokeswoman.
Holmes faces 165 counts, including murder and attempted murder charges, but there have already been some notable legal battles in the run-up to the actual trial.
In March 2013, Holmes offered to plead guilty so he could avoid the death penalty, a deal the district attorney declined.
A few months later, a judge ruled that Holmes had to be restrained during the trial
, via a hidden harness anchored to the floor. The defense filed an objection, conceding that Holmes exacted the violence but blaming his actions on mental illness.
"Mr. Holmes suffers from a severe mental illness and was in the throes of a psychotic episode when he committed the acts that resulted in the tragic loss of life and injuries sustained by movie goers on July 20, 2012," the motion said.
Judge Carlos Samour last year ordered Holmes to submit to an additional sanity exam
, saying that the previous test, conducted in 2013 at the Colorado Mental Health Institute at Pueblo, was "incomplete and inadequate."
Jury selection began in January, and after a four-month process
, 12 jurors and alternates, composed of 19 women and five men, were selected.