By Keith Coffman

CENTENNIAL, Colo., (Reuters) - Colorado theater gunman James Holmes told a court-appointed psychiatrist that he believed his suicidal thoughts would go away if he killed other people, jurors in his murder trial heard on Friday.

In a videotaped session with psychiatrist William Reid shown to the jury, the former neuroscience graduate student talked about being depressed and described how he began acquiring weapons in the months leading up to the July 2012 massacre.

"I kind of transferred it (suicide) to homicidal thoughts," he said, adding that the compulsion to kill became consuming.

The 27-year-old California native could face the death penalty if he is convicted of killing 12 moviegoers and wounding dozens more during a screening of the Batman film "The Dark Knight Rises."

Holmes has pleaded not guilty by reason of insanity to multiple counts of first-degree murder, attempted murder and explosives charges stemming from the rampage. His lawyers said he suffers from schizophrenia.

Reid, who testified this week, said that after interviewing Holmes for 22 hours, he concluded the defendant was sane when he planned and carried out the massacre.

Holmes responded to questions from Reid in the interviews conducted last year with clipped answers as he went through his thought process.

He said after buying a .40-caliber pistol, he felt compelled to use it in a "mass murder situation." He later purchased another handgun, along with a pump-action shotgun and a semiautomatic rifle, all of which were recovered from the crime scene in the Denver suburb of Aurora.

At one point, he said, he thought the FBI might be watching him as he planned the mass killing. If FBI agents found out about his plot, "they could have done the right thing ... and locked me up," he said.

When asked why he picked the Colorado premiere of the Batman movie for his attack, Holmes said: "I knew it would be a blockbuster and there would be a lot of people there."

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Holmes also talked about his life behind bars. Although he is kept away from the general jail population, he said he sometimes hears other inmates call him a "baby-killer and stuff."

Six-year-old Veronica Moser-Sullivan was the youngest victim killed in the rampage.

In an earlier videotaped session played in court, Holmes said he sometimes cries before he falls asleep at night over "regrets" he has about the shootings.

(Editing by Cynthia Johnston and Mohammad Zargham)