CENTENNIAL, Colorado — The police officer who arrested Colorado movie theater massacre gunman James Holmes told jurors Thursday the shooter seemed very calm, relaxed and “sort of disconnected” when he found him standing behind the cinema where he had killed 12 people.

Holmes, 27, is charged with multiple counts of murder and attempted murder for opening fire inside a packed midnight premiere of the Batman film “The Dark Knight Rises” at a Denver-area multiplex in July 2012, also wounding 70 people.

The former neuroscience graduate student has pleaded not guilty by reason of insanity. Prosecutors say they will seek the death penalty if he is convicted.

Aurora police officer Jason Oviatt told the court he found Holmes next to his white sedan wearing a gas mask, helmet and body armor. He thought at first the defendant was a fellow officer, but realized he was acting oddly and ordered him to his knees.

“He was sort of vacant. He was very relaxed. He was very calm and sort of disconnected … not displaying any outward emotion or any outward sign of real engagement in what’s going on,” Oviatt told the jury.

“He was very sweaty. He smelled bad.”

Asked whether Holmes had any problems answering questions put to him by officers, Oviatt replied: “Not at all.”

He also described Holmes’s response when asked by another officer if he had an accomplice.

“He said: ‘It’s just me,’” Oviatt told the court.

The officer described the siren- and scream-filled period after he put Holmes in a patrol car as something of a blur.

“A lot of people being carried to cars, a lot of blood,” he said, adding he stayed by the vehicle holding Holmes.

“I didn’t want a victim from the theater to be put into the same car,” Oviatt said, pausing to get a handle on his emotions. “I didn’t want him to be taken to the hospital. I didn’t want him to escape while no one was paying attention.”

Another police officer, Aaron Blue, said he asked Holmes if he had any weapons, and that he replied: “I have four guns. I have improvised explosive devices, and they won’t go off unless you set them off.”

Prosecutors say Holmes rigged his apartment near the theater with explosives, which were defused by bomb technicians.

Police Sgt. Stephen Redfearn said the suspect moved around a lot in the patrol car, making him nervous, and he said he was struck by how Holmes seemed “very interested” in what was going on as they treated the wounded nearby.

The court was shown security camera footage of Holmes inside the Century 16 multiplex before the attack and of terrified patrons running through the lobby after the shooting started.

A homicide detective then showed a series of photographs, going row by row through theater nine, the bodies of the victims lying where they fell.

A succession of burly police officers and firefighters have fought back tears on the witness stand this week as they described the aftermath of the attack.

Police officer Justin Grizzle drove several victims to the hospital, including Caleb Medley, an aspiring stand-up comedian who was “unrecognizable” after being shot in the face.

“He made some of the most awful noises I’ve ever heard. I could tell he was dying. I could tell he was gurgling on his own blood,” Grizzle told the court, between sobs and long pauses.

“And then he would stop and I heard nothing. So I yelled at him: ‘Don’t f—- die on me! Don’t f—- die on me!’ And he would start breathing again, and I would start breathing again, and we’d continue.”

Medley survived after multiple surgeries, and he testified in court on Tuesday from a wheelchair, using an alphabet board to spell out answers. Sitting just feet away, Holmes looked on, expressionless.

Prosecutors say Holmes, who was armed with a pistol, shotgun and semiautomatic rifle, did it because he had lost his career, girlfriend and purpose in life.

Holmes’ public defenders say he was suffering from schizophrenia, that he heard voices commanding him to kill and was not in control of his actions.

The trial is expected to last four or five months.