( CNN ) Seven minutes after an Aurora , Colorado , theatergoer called 911 to report a massacre in progress , suspect James Holmes surrendered to police , a dozen dead bodies allegedly in his wake . 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 .
Carlos Samour has pleaded not guilty by reason of insanity in the 2012 theater shooting . His trial begins Monday , and Homes faces 165 counts , including murder and attempted murder .