A logical place to look was online. However, one thing became apparent early on: Holmes has very few digital footprints.
No Facebook account. No Twitter account. Not even a mention of him in an article or Google search. No physical address listing. So far ABC News has only been able to find his email address at the University of Colorado Denver. TMZ reported it was also able to dig up an old MySpace photo, though it said he apparently had no real MySpace friends.
Holmes may be different from other alleged shooters. The man arrested in the Gabrielle Giffords shooting, Jared Loughner, had a MySpace page and a YouTube account. Anders Breivik, accused of killing 77 people in Norway, published a manifesto online. Holmes, in contrast, appears to be what some call "Web dead."
While it is possible that Holmes simply didn't have much of an online identity, it seems unlikely that he had no online fingerprints at all. Some experts suggest an online identity under a pseudonym may emerge, or that Holmes, as a tech-savvy graduate student, limited himself university communications that were password-protected.
"It could be that he is using a different name online or some variation of his name or another name entirely," Eva Galperin, International Freedom of Expression Coordinator at the Electronic Frontier Foundation, told ABC News. "He could have a significant online presence and we would not know about it."
Other sources, who asked not to be quoted by name, made the same point.
Many sites and social media services, like Facebook and Google Plus, have policies requiring users to go by their real names. However, if the name you use looks real and isn't flagged, you can easily get away without giving away your true identity.
There is also the possibility that Holmes worked hard to erase his identity online, but experts think that's unlikely.
"It is very hard to have no digital footprint right now," Michael Fertik, the CEO and founder of Reputation.com, told ABC News. "What my company stands for is creating the digital footprint you want."
Fertik said it would be very hard for Holmes to have left no online or digital traces over recent years. "It would be very unusual for a 24-year-old to have nothing on the Internet. My guess is that we don't know what name he was using online."
A service like Reputation.com or Removeyourname.com would help clear some of the history, but not all of it, Fertik said.
James Holmes is a common name, which complicates things. In the hours after Holmes was named as the suspect, people flocked to Facebook and Twitter to learn more about Holmes. Another James Holmes living in Littleton, Colorado had his Facebook page flooded with comments.
"I appreciate the fact that you are trying to become better-informed about the occurrences last night in Aurora, but you have been somewhat mislead, in that I am not the man who did it," the other James Holmes wrote on his Facebook wall. "I am not a 24-year-old gun-slinging killer from Aurora, I am a 22-year old book-slinging mass eater from Littleton." He signed the message "Regards, A different guy named James Holmes."
Whether he has a common name or not, James Holmes does have a background. It may just not be one easily found through a computer.
"Generally the way intelligence surfaces is by looking at the person's social networks -- not Facebook or Google Plus -- but looking at their friends or real-life contacts," Eva Galperin said.