James Holmes was charged with 24 counts of murder Monday in the deaths of 12 people at a Batman movie premiere in Aurora, Colo.
The murder charges included 1 count of murder, and 1 counts of "murder of extreme indifference," for each of the victims, according to NBC's Mike Taibbi.
Holmes was also formally charged with 116 counts of attempted murder, according to The Associated Press.
A former University of Colorado graduate student, Holmes is accused of carrying out the bloody attack on moviegoers at the midnight premiere of "A Dark Knight Rises" on July 20, and wiring his apartment with enough explosives to have leveled the building if they had detonated.
The trial could turn on questions of Holmes' state of mind. "I don't think it's too hard to predict the path of this proceeding," said Craig Silverman, a former chief deputy district attorney in Denver. "This is not a whodunit. ... The only possible defense is insanity."
According to the law in Colorado, defendants are not legally liable for their acts if they cannot differentiate between right and wrong, the report said. However, "care should be taken not to confuse such mental disease or defect with moral obliquity, mental depravity, or passion growing out of anger, revenge, hatred, or other motives, and kindred evil conditions," the law stipulates, the AP said.
Holmes was enrolled in the University of Colorado Ph.D. neuroscience program but withdrew last month. Neighbors said withdrawal from the program would likely have triggered his eviction from the building, which is reserved for people affiliated with the school.
Investigators said Holmes had amassed weapons, ammunition and explosives over the course of several months.
He was arrested in the parking lot of the movie theater shortly after the shootings, and told officers his apartment contained explosives, police said. That information prompted evacuation of Holmes' apartment building and those surrounding it until law enforcement teams could disarm the jumble of wires and explosive devices set to detonate by trip wires.
In his initial court appearance, Holmes was dressed in red prison garb, and had his hair dyed bright red. He looked off into the distance or down at the table, at times knitting his brow in a quizical expression or as if he was trying to concentrate. He did not speak.