Though there are indications that something may have been amiss in Holmes' life in recent months.

He withdrew from the program in June 2012, though "he gave no reason for his withdrawal from the graduate school," said Jacque Montgomery, spokeswoman for the University of Colorado.

It is not immediately clear if Holmes, who also worked in a paid position in the university's neuroscience research program, was still employed there after withdrawing from the program.

Holmes received a large volume of deliveries over the past four months to both his home and work addresses, which police believe begins to explain how he got his hands on some of the materials used in the rampage and the subsequent discovery of his booby-trapped apartment, Aurora Police Chief Paul Oates.

The police chief has declined to release details about a possible motive or Holmes' appearance at the time of his arrest, citing an ongoing investigation. But he did say Holmes purchased four weapons and more than 6,000 rounds of ammunition in recent months.

Police allege Holmes was dressed in black, wearing a ballistic helmet, a tactical ballistic vest, protective leggings, a throat and groin protector and a gas mask during the attack. Witnesses to the shooting say because the gunman wore a gas mask, they did not see his face.

Unlike most people his age, Holmes does not appear to have a social media footprint -- no Facebook, no Twitter and no Tumblr account, though authorities are investigating whether he posted a profile on sex website Adult Friend Finder.

The profile contains a picture of a man with fiery red hair, a law enforcement source said. Police believe it may be a picture of Holmes, said the source, who was not authorized to speak to the media. The profile said it was created by a 24-year-old man from Aurora and has since been taken down.

It's a profile that contrasts with news that Holmes worked as a counselor at a summer camp for needy children in 2008.

Camp Max Straus caters to needy children ages 7-14, and is run by Jewish Big Brothers Big Sisters of Los Angeles, which confirmed his employment but would not offer further details or comment.