This claim is specious at best. He didn't lack a footprint. Because of the commonality of his name, it is more like his footprint is buried by hundreds upon hundreds of other footprints and it will take longer to find his particular footprint.
Take Facebook for example. A search on the name James Holmes yields hundreds of results. Many of these results come up with profiles that have high security settings so you can't see profile images (or they are not actual 'person' images but another avatar) or locations. His footprint there could be buried by all the other James Holmes.
There is also the case where he may go by a different handle on the internet. For example, he seemed to have an obsession with The Joker, so he may have used the name behind the make-up from the 89 movie- Jack Napier. Again, a search on Facebook comes up with hundreds upon hundreds of accounts using that handle.
It may be a long time before we find his footprint unless a friend or classmate comes forward to provide a unique identifier to his online footprint.
He shows up in Intelius, with matching residences and parental names as James “C” Holmes.
Unusual mistake or deliberate?