Colorado movie massacre gunman James Holmes was found guilty on Thursday of multiple counts of murder in the first degree, a verdict that enables prosecutors to seek the death penalty for the former graduate student who killed a dozen people and wounded 70 at a midnight premiere of a Batman film in 2012.

After a three-month trial in which they were presented with thousands of pieces of evidence and testimony from hundreds of witnesses, jurors deliberated for about a day and a half, then handed prosecutors a big win. The panel of nine women and three men rejected the defense's claim that Holmes was legally insane.

The trial now enters the punishment phase, when the jury must determine whether Holmes, 27, should be put to death or serve a mandatory life sentence with no possibility of parole.

The defense conceded that Holmes was the shooter, but presented expert witnesses who testified that the former neuroscience student was not in control of his actions because he suffered from schizophrenia and heard voices ordering him to kill.

The prosecution presented two court-appointed psychiatrists who concluded Holmes was legally sane when he plotted and carried out the July 2012 rampage at a multiplex in the Denver suburb of Aurora.

District Attorney George Brauchler said the gunman was unusually intelligent but socially inept, and harbored a long-standing hatred of humanity.

Brauchler said Holmes could not take it when he did poorly on exams at the University of Colorado, and broke up with the only girlfriend he had ever been intimate with.

The prosecution argued that Holmes' detailed preparations for the attack showed he knew what he was doing, and knew it was wrong. They presented evidence about his purchases of guns, tear gas and body armor. They also showed how he conducted online research into bomb-making so he could booby-trap his apartment before he left for the cinema.

Holmes rigged the bombs and turned loud music on the stereo, hoping someone would open the door and trigger a deadly blast. The devices were later defused by a police bomb squad.

Sobs filled the courtroom during the trial as dozens of wounded survivors testified about hiding behind plastic chairs from the hail of bullets, and stumbling over the bodies of loved ones as they fled the theater.

Brauchler showed photos of the dead during his closing argument. His voice broke and he wiped his eyes.

“That guy, sitting right there,” he said, pointing at Holmes. “He did this.”