A 12-person jury which includes 12 alternates, among them two survivors of the 1999 Columbine shooting, has been seated in the death penalty trial of suspected Colorado movie theater shooter James Holmes.

The jurors were finalized and sworn on Tuesday afternoon after being selected from an unprecedented 9,000-member jury pool, the largest in U.S. history. The nearly all-white panel consists of five men and 19 women. One of the women is Hispanic.

Among the jury are a dental assistant instructor, young mother of three, physicist and competitive shooter, and store manager at Bed Bath and Beyond, NBC News reports. In addition, a union plumber, schoolteacher, Denver Public Schools employees, a business woman and a person suffering from depression will also serve on the jury panel, reports MSNBC.

Holmes, 27, is accused of killing 12 movie goers and wounding 70 others at an Aurora theater showing the "Dark Knight" movie on July 20, 2012. It is up to the jury to determine whether or not he was sane or insane during the shooting. They will also decide whether to sentence him to death or life in prison if he is found guilty.

On Tuesday, District Attorney George Brauchler warned jurors that the trial will be a "four- to five-month roller coaster through the worst haunted house you can imagine," according to the Associated Press.

Rather than arguing that Holmes was not responsible for the shooting, the defense team will argue that he was in the middle of a psychotic episode, according to the AP.

The jurors are scheduled to appear in court for opening statements on April 27.

In December 2014, the parents of Holmes released a statement asking for his life to be spared from execution on the grounds that he suffers from mental illness.

"He is a human being gripped by a severe mental illness," reads the letter, according to AP. "We have always loved him, and we do not want him to be executed."

His parents, who live in California, added they rather avoid a traumatic trial and strike a deal that calls for a guilty plea in exchange for a sentence of life in prison without parole.

"If that happened, our son would be in prison the rest of his life, but no one would have to relive those horrible events at a trial the media has permission to televise," the parents wrote.

They also said that the best option would be sending their son to a mental institution if he is found not guilty by reason of insanity.