District Judge Carlos A. Samour Jr. denied requests from prosecutors and the defense to close all or part of the process, saying openness and media scrutiny will "enhance the reliability and fairness of the process."
Jury selection is scheduled to start Oct. 14 for the trial of James Holmes, who pleaded not guilty by reason of insanity to killing 12 people and injuring 70 in the July 2012 attack. Prosecutors are seeking the death penalty.
The defense argued the jury selection process should be closed to protect potential jurors from harassment about their answers and preserve Holmes' right to a fair trial.
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Defense lawyer Daniel King suggested a redacted transcript could be released after a jury is chosen, with prospective jurors' names blacked out.
Prosecutors argued that individual questioning should be closed to prevent potential jurors from learning through media reports what they would be asked. But they said the public and reporters should be allowed to attend when potential jurors are questioned as a group.
Media organizations, including The Associated Press, argued an open jury selection would not preclude Holmes from getting a fair trial.
In his 29-page ruling, Samour said prospective jurors will be referred to in public by number, not by their names, although he and the attorneys would know their identities. The same system will be used during the trial, he said.
Samour also said a questionnaire that prospective jurors will fill out will not be made public, nor will their answers.
The judge wants to seat 12 jurors and 12 alternates.
He plans to issue 6,000 summonses and expects 3,300 people will respond. After prospective jurors fill out the questionnaire and are questioned individually, Samour said, he hopes to have a pool of 100 to 120 people from which to choose the final 24.
Samour has said jury selection could take up to three months, and the trial another five months.