Colorado movie shooter James Holmes is sane and meticulously planned his rampage: psychiatrist

The meticulous planning Colorado movie theater gunman James Holmes went through to hide his intentions to commit mass murder and cause maximum carnage showed he was sane at the time, a psychiatrist testified in his murder trial on Thursday.

But court-appointed psychiatrist William Reid admitted under questioning from a defense lawyer that the shooting rampage would not have happened were it not for the defendant's serious mental illness.

Holmes, 27, has pleaded not guilty by reason of insanity to killing 12 moviegoers and wounding 70 others inside a Denver-area cinema during a viewing of the Batman film "The Dark Knight Rises" in 2012.

Prosecutors have charged Holmes with multiple counts of first-degree murder and attempted murder, and have said they will seek the death penalty for the Californian if he is convicted.

Arapahoe County District Court Judge Carlos Samour appointed Reid to conduct a mental evaluation of the former neuroscience graduate student after he concluded a first sanity examination was deficient.

The exchange between Reid and public defender Daniel King came after jurors in the capital case spent nearly a week watching 22 hours of videotaped interviews the psychiatrist conducted with the admitted shooter last year.

"The question is not if whether Mr. Holmes' mental illness affected his thinking but to what extent," King said. "Absent his mental illness we wouldn't be here at all."

"That's true," Reid said in response.

Reid said he diagnosed the 27-year-old with schizotypal personality disorder, short of full-blown schizophrenia - what defense lawyers have said he suffers from.

Under questioning by prosecutor George Brauchler, Reid testified that Holmes went to great lengths to hide his plot from others, cased the multiplex to find the optimum theater to attack, and chose weapons that would cause maximum death.

"I don't believe he had a serious psychotic break prior to the shootings," Reid said. "He had the capacity to know that the shootings were highly illegal (and) knew beforehand his victims would suffer."

King was scheduled to resume his cross-examination of Reid on Friday.