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 had pleaded not guilty by reason of insanity. Prosecutors say they will seek the death penalty if he is convicted.
On day four of the trial, the prosecution called Aurora police officer Jason Oviatt, who found Holmes next to his car outside the theater wearing a gas mask, helmet and body armor.
Oviatt thought at first that the defendant was a fellow officer, because of his dress. But the police officer 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 of 19 women and five men.
"He was very sweaty. He smelled bad."
Asked twice by the prosecution whether Holmes had any apparent problems answering questions put to him by officers, Oviatt responded: "Not at all."
He described searching the suspect and finding two knives and loaded pistol-ammunition clips, but said he was hindered by the amount of body armor Holmes was wearing.
'IT'S JUST ME'
Oviatt also repeated key testimony given at a preliminary hearing in 2013, describing Holmes's response when asked by another officer if he had an accomplice.
"He said: 'It's just me,'" Oviatt told the court.
Oviatt said he also heard Holmes tell another officer that things in his apartment were set to go off "if you trip them," which Oviatt said he took to mean bombs or booby traps.
Prosecutors say Holmes rigged his apartment near the theater with explosives, which were defused by bomb technicians.
Oviatt described the siren- and scream-filled period after he put Holmes in a patrol car as something of a blur.
"A lot 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 that he was in," 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."
Prosecutors say Holmes, who was armed with a pistol, shotgun and semiautomatic rifle, tried to murder a theater full of people because he had lost his career, girlfriend and purpose in life, and that he did it "to make himself feel better."
Holmes' public defenders say he was suffering from schizophrenia; that since high school he had heard voices in his head commanding him to kill; and that he was not in control of his actions "or what he perceived to be reality."
The trial is expected to last four or five months.
