AURORA, Colo. – University of Colorado officials were looking Sunday into whether James Holmes used his position in a graduate program to collect hazardous materials, but school officials weren’t saying whether they knew the suspect in a movie theater massacre was anything more than a hard-working student.

Law enforcement officials also revealed that Holmes, 24, has not been cooperating with them and that it could take months to learn what prompted the attack early Friday on a packed theater of moviegoers watching the premiere of the latest Batman movie. The assault killed 12 and left 59 wounded.

Investigators found a Batman mask inside Holmes’ apartment after they finished clearing the home of booby traps and ammunition, a law enforcement official close to the investigation said Sunday on the condition of anonymity because he was not authorized to speak to the media.