CENTENNIAL, Colo. — The movie theater was a blood-soaked nightmare that night in July. Wounded moviegoers screamed for help and tried to crawl for the exits. Bodies lay in the aisles. The floor was a carpet of shell casings, the air stung with the smell of tear gas, and dozens of abandoned cellphones bleated incessantly.

But outside, James E. Holmes stood with eerie calm, his head hidden behind a gas mask and helmet, his hands resting on the roof of his car. He was, police officers recalled here in court on Monday, detached from the chaos he had created moments before. He was sweating heavily underneath a sheath of black body armor. He smelled foul.

“He was very, very relaxed,” said Officer Jason Oviatt of the Aurora Police Department, who apprehended Mr. Holmes behind the theater minutes after the shooting. “It was like there weren’t normal emotional responses. He seemed very detached from it all.”

Officer Oviatt was one of six police officers to testify here on the first day of a preliminary hearing to determine whether there is enough evidence to try Mr. Holmes, 25, for killing 12 people and wounding dozens more inside the Century 16 movie theater in Aurora, a Denver suburb. An Arapahoe County district judge, William B. Sylvester, will make that decision.