The families of victims last year's mass shooting at a Colorado theater shooting sat through emotional testimony Monday from police officers who tried to save the lives of the wounded.

One sergeant recalled during the hearing for suspected gunman James Holmes that he checked and did not find a pulse for the youngest victim, 6-year-old Veronica Moser-Sullivan.

Another who drove the wounded to the hospital said he had to stop one man worried about his 7-year-old daughter from jumping out of the moving patrol car.

A bearded Holmes didn't appear to show any emotion. One woman sat with her head buried in her hands during the testimony about Veronica.

The police officer who arrested the suspected gunman said he first thought James Holmes was a fellow officer because he was wearing body armor.

Then the officer realized he was wrong because Holmes wasn't running toward the scene.

The first extensive details were emerging about the young man suspected of killing 12 people and wounding at least 58 in one of the worst mass shootings in the U.S. last year. The hearing will determine whether the case will go to trial.

Holmes is charged with more than 160 counts, including murder and attempted murder. Investigators say he was wearing a gas mask, in addition to the body armor, when he tossed two gas canisters and opened fire in the theater on July 20.

As soon as Officer Jason Oviatt saw Holmes outside the theater and realized that he wasn't a fellow officer, he pointed his gun at Holmes, handcuffed him and searched him. Oviatt said he found two knives and a semi-automatic handgun on top of Holmes' car. The officer said an ammunition round fell out of Holmes' pocket, and he found another one on the ground.

Police officers who arrested Holmes described him as unusually relaxed but fidgety at times. They said he told them that his apartment had been booby trapped.

Holmes didn't seem to have "normal emotional reactions" to things, Oviatt said. "He seemed very detached from it all," he said.

Until now, many details of the case have been kept quiet. Three days after the shooting, District Judge William Sylvester forbade attorneys and investigators from discussing the case publicly, and many court documents have been filed under seal.

Police say Holmes, now 25, had stockpiled weapons, ammunition and explosives. He was a first-year student in a Ph.D. neuroscience program at the University of Colorado, Denver, but he failed a year-end exam and withdrew, authorities have said.

The shootings came six weeks later.

Federal authorities have said Holmes entered the theater with a ticket and is believed to have propped open a door, slipped out to his car and returned with his weapons. Police arrested him outside the theater shortly after the shootings ended.

Legal analysts said that evidence appears to be so strong that Holmes may accept a plea agreement before trial. In general, plea agreements help prosecutors avoid costly trials, give the accused a lesser sentence like life in prison rather than the death penalty and spare the victims and their families from the trauma of going through a lengthy trial.

Holmes' mental health could be a significant issue in the hearing.

His attorneys have told the judge Holmes is mentally ill, but they have not said whether they plan to employ an insanity defense. He had seen a university psychiatrist, and his lawyers have said he tried to call the psychiatrist nine minutes before the killing began.

Defense lawyers have said they plan to call at least two witnesses who could testify about Holmes' mental health. Prosecutors asked the judge to block the witnesses, but he refused.

Lawyers have been debating what physical evidence should be made available, whether a psychiatrist who met with Holmes is barred from testimony by doctor-patient privilege and other issues.

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Associated Press writer Dan Elliott contributed.