Now the life of the 24-year-old is being examined by the police as they try to understand what led him to open fire in the packed screening.
His family lives in San Diego, California and have said: "Our hearts go out to those who were involved in this tragedy and to the families and friends of those involved."
His father, Robert Holmes, was seen leaving the family home with an overnight bag. Local reports suggested he was heading to Colorado.
His son, James Holmes, attended high school in San Diego and then continued his studies at the University of California Riverside.
The director of media relations, Kris Lovekin, said: "We are confirming that James Eagan Holmes does appear in our records.
"He graduated in Spring 2010 with a degree in Neuroscience. Last address we have for him is in San Diego."
In fact, James Holmes left California soon after and travelled east to study at the University of Colorado Medical School.
He arrived in June 2011 and enrolled on the Neurosciences program at the Anschutz Medical campus in Aurora.
Last month he withdrew from the course but the Medical School has been unable to provide more details as to why.
They would not discuss whether there had been any disciplinary issues.
The apartment block where James Holmes has been living in Aurora is now at the centre of a security alert after he reportedly told police that there were explosives inside.
A pharmacy student who lives in the same building told the Denver Post newspaper he had called the emergency services at 12.30am local time because there was a song blaring from the stereo inside apartment 10, where Holmes lived.
This was around the time of the shooting in the cinema.
The neighbour reported that he couldn't identify the track but said it seemed to be stuck playing on repeat.
He also said Holmes was quite private and wouldn't acknowledge people when they passed in the hall.
"No one knew him. No one," he said.
Journalist John Harding, speaking outside Holmes' apartment, reported that the booby trap was a "sophisticated device" including trip-wires and bottles filled with unknown liquids.
The operation to make the building safe is continuing, as Holmes remains in police custody.