James Eagan Holmes, 24, who allegedly opened fire with an assault rifle, shotgun and handgun on a crowded showing of the new Batman movie, "The Dark Knight Rises," was a doctoral candidate at the University of Colorado in Denver.
Twelve people were killed and 59 injured, 16 critically, in the midnight-showing rampage at an Aurora, Colo., mall movieplex. He also left his apartment booby-trapped, police said.
Police had given no motive for the shooting.
The Washington Post quoted a University of Colorado faculty member who asked not to be identified as saying Holmes, who was studying to be a neuroscientist, had performed poorly on spring exams and decided to quit the program.
"The University of Colorado Denver-Aschutz Medical Campus can confirm that Holmes was in the process of withdrawing from the University of Colorado Denver's graduate program in neurosciences," the university said in a release.
U-T San Diego reported Holmes grew up in the Rancho Penasquitos area of San Diego and graduated from Westview High School in 2006. He earned his bachelor's degree in neuroscience from the University of California, Riverside.
Holmes' family issued a statement saying their "hearts go out to those who were involved in this tragedy and to the families and friends of those involved. ... We are still trying to process this information."
The Web site said Holmes' mother, Arlen, is a registered nurse and his father, Robert, is a software engineer.
Neighbors described Holmes as a loner.
"He was quiet, didn't seem to have lots of friends," Anthony Mai, 16, told U-T San Diego.
Claire Sampankanpanich, a third-year Johns Hopkins University medical student, said she attended a biotechonology book camp with Holmes at Miramar College.
"A lot of us didn't get along very well with him," she said. "He didn't talk to a lot of us, but when he did he was kind of a smart alec. He didn't want to work with any of us."