03/05/2015 04:14 EST | Updated 05/05/2015 05:59 EDT

Judge sets tentative dates in April for opening statements in Colorado theatre shooting trial

CENTENNIAL, Colo. - With jury selection moving faster than expected, a judge on Thursday set two possible dates in April for opening statements in the Colorado theatre shooting case.

The trial had been expected to open in May or early June, but Judge Carlos A. Samour Jr. tentatively scheduled the start of the death penalty case for April 21 or April 27.

Jury selection began Jan. 20 and attorneys have been questioning prospective jurors about their views on capital punishment, mental illness and other issues.

Defendant James Holmes has pleaded not guilty by reason of insanity to charges of killing 12 people and injuring 70 in the July 20, 2012, shooting. If jurors decide he was sane during the attack, they would then determine punishment.

Jury selection has been a testament to the logistical hurdles of trying a case of a mass shooter who survives his attack.

About 9,000 prospective jurors were summoned in what experts called the biggest jury pool in U.S. history. The figure was nearly nine times the number summoned in the Boston marathon bombing trial.

During the first phase, thousands of people filled out lengthy questionnaires and Samour dismissed more than 1,000 who brought doctors' notes, weren't U.S. citizens, had family problems or weren't Arapahoe County residents.

Hundreds were asked to return for individual questioning that began Feb. 11.

Thus far, Samour has asked more than 50 prospective jurors to return for the next round of screening in which he hopes to find a pool of 120 people to winnow to 12 jurors and 12 alternates.