CENTENNIAL — They shuffled into the courtroom in a nervous procession: an older man in plaid flannel, a middle-aged woman with curls, a young man with hair pressed into a fauxhawk.

One by one Tuesday, the first prospective jurors for the Aurora movie theater murder trial walked to their seats with their eyes cast down, none appearing to sneak a glimpse to their left of the bearded and bespectacled man on trial for the attack — the man whose life they may soon be asked to condemn or to spare.

“No one should assume that Mr. Holmes committed a crime just because he has been charged in this case,” Judge Carlos Samour read to the jurors from the script that he will use to address similar groups of jurors over the next four weeks. “Mr. Holmes is presumed innocent.”

Thus officially began the trial for one of the worst mass shootings in American history.

Two and a half years to the day after James Holmes killed 12 people and wounded 70 others inside the Century Aurora 16 movie theater, prosecutors, defense attorneys and Samour began the process of picking the people who will decide his fate. It was a date that had been set and reset five times during the course of the case, and Samour’s voice carried a note of purpose when he opened a quick hearing Tuesday morning with these words: “The case is set today for trial.”

Just shy of 190 jurors were expected at the courthouse Tuesday afternoon in the first wave to be called. They listened to remarks from Samour — in which he told them not to talk to anyone about the case or research its details.

They filled out 18-page questionnaires covering their backgrounds, as well as their views on the death penalty, mental illness and the criminal justice system. Then they went home to wait to learn whether they will be called back.

Attorneys will start reviewing the first completed questionnaires on Wednesday, and Samour urged both sides “to be sensible and reasonable when stipulating to the excusal of jurors.”

“We are going to be spending a lot of time with each other,” Samour said at a morning hearing to go over the jury-selection plan. “My expectation is that everybody will make a good-faith effort to work together.”

By the end of the day, Samour had released seven jurors from service, a crawling progress that seemed only to underscore the difficult process ahead. Four of the excused jurors had provided proof that they live outside Arapahoe County; two had offered doctor’s notes; and one arrived at the wrong time and was accidentally dismissed with a group of jurors who had been called for other cases.

Samour had summoned an unprecedented 9,000 jurors for the case, but he announced Tuesday that the pool already has dwindled to 7,000. He said 2,000 summonses had been returned as undeliverable.

A heavy police presence massed outside the Arapahoe County courthouse ahead of Tuesday’s hearings. Arapahoe County sheriff’s patrol cars and unmarked vans blocked areas of the busy parking lot. Two sheriff’s deputies were posted on the courthouse’s roof.

Television satellite trucks and other media vehicles filled two back rows of the parking lot. Reporters and photographers lined the bright yellow barriers placed along the sidewalks.

The prospective jurors began arriving around noon, clutching their jury summonses in their hands, and by 2 p.m. they filled almost every seat in the courtroom where Holmes’ trial will play out.

For the first time since his arrest, Holmes appeared in court wearing dress clothes, not the red jail jumpsuits of prior hearings. He wore tan slacks and an untucked blue-and-white-striped button shirt. He had a dark sport coat, clean-cut hair, a beard and glasses. A cable winding down his pant leg from his waist discretely tethered him to the floor.

Holmes sat impassively as Samour told jurors of the charges: “Mr. Holmes has been charged with the murders of 12 people and the attempted murders of 70 people at the Century 16 Theatres located at 14300 E. Alameda Ave., Aurora, Colo., on July 20, 2012.”

Holmes appeared expressionless when Samour explained that the suspect has pleaded not guilty by reason of insanity and that prosecutors are seeking the death penalty. And, when the jurors left the courtroom for a break, Holmes remained seated, staring forward.

“I want to express my gratitude again for your willingness to do your civic duty today,” Samour said, concluding his remarks to the jurors. “Without the rule of law, our democracy could not thrive.”

Reporter Jordan Steffen contributed to this report.

John Ingold: 303-954-1068, jingold@denverpost.com or twitter.com/johningold