James Holmes, the suspect in the Colorado shooting rampage, is described as a quiet, standoffish medical student from San Diego who recently dropped out of a doctoral program at the University of Colorado medical school.

A profile of the 24-year-old suspect is beginning to emerge hours after a gunman opened fire in a crowded movie theater showing the new Batman film, The Dark Knight Rises, killing 12 people.

USA TODAY's Kevin Johnson quotes federal law enforcement officials as confirming the identity of the shooting suspect as Holmes, but he apparently did not have a record.

The Denver Post, citing "information provided" to the newspaper, reports that the suspect described himself last year in an apartment rental application as a student who was "quiet and easygoing."

Denver's Fox31 says police documents show he moved to Colorado from San Diego to pursue a Ph.D. in Denver.

The Associated Press reports that Holmes began a program in neurosciences at the University of Colorado in the fall of 2011 but withdrew last month.

University spokeswoman Jacque Montgomery confirms Holmes was a graduate student at the school of medicine until last month. On May 8, he was scheduled to present a paper on MicroRNA biomarkers for a class on psychiatric and neurological disorders.

The suspect, dressed in black and wearing a protective vest, was arrested by police near his car behind the movie theater during a midnight showing of the Batman film. They seized an assault rifle, shotgun and two pistols at the scene, the Associated Press reports.

"He did not resist. He did not put up a fight," says Aurora police spokesman Frank Fania.

New York Police Commissioner Ray Kelly, who was in touch with Colorado authorities, said the gunman had dyed his hair red and called himself "The Joker," referring to Batman's arch-nemesis.

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Colo. suspect is medical school dropout