James Holmes, the suspect in the shooting rampage at a Colorado movie theatre, has been described in various media reports as a brilliant academic who is introverted and shy - a "loner."

That same label was applied to Seung-Hui Cho, the Virginia Tech student who gunned down 32 people on campus in 2007, and Jared Loughner, the young man suspected of shooting six dead at a Tucson, Ariz., mall in 2011.

But expert opinion appears to be divided over the strength of the correlation between being a loner and being a mass killer.

In a commentary published last year on the website of Psychology Today titled Let's Stop Stereotyping Loners, Steven Reiss, a professor emeritus of psychology at Ohio State University, wrote that the media have done a "disservice" by perpetuating the idea that people who are asocial are dangerous.

"Whether a person is a loner, gregarious, or in between, tells us absolutely nothing about how dangerous that person might be," he wrote.

This weekend, in the wake of the shooting that killed 12 people and wounded 58 others during a screening of the new Batman movie, Reiss followed up with another blog entry, writing that he thinks loners are "normal people."

In trying to predict whether someone is predisposed toward violence, it is more important, he said, to examine their values than how many friends they have.

"The person predisposed toward violence has an unusually high valuation of winning/aggression, and unusually low valuations of honour and idealism," he wrote.

But on the same website, Stanton Peele, a psychologist and addiction specialist in New Jersey, posted a contrary blog suggesting social isolation is relevant when examining what causes people to commit acts of violence.

"If (the suspect) had someone to go to the movies with, he wouldn't have faced a crowded theatre with guns blazing," he wrote. "Being alone is bad for mental health and makes people more likely to commit antisocial acts."

Time and again, Peele wrote, there have been examples of killers whose social isolation left them with no social bearings to guide their behaviour, no one to turn to with their problems and time on their hands to "allow their feelings of rejection to fester."

Holmes, 24, looked dazed Monday as he made his first court appearance in the Denver suburb of Aurora. Authorities have said Holmes is refusing to co-operate and it could take months to learn what prompted one of the worst mass shootings in U.S. history.

The former graduate neuroscience student is accused of setting off gas canisters and opening fire upon theatregoers with a semi-automatic rifle, shotgun and pistol. He reportedly identified himself as The Joker - an apparent reference to the Batman villain - when confronted by police.

Holmes, who will be formally charged next week, could face the death penalty.

The portrait that has emerged of the suspected killer is far from complete. One doctoral student at the University of Colorado told Reuters that references to Holmes as a "loner" are unfair and that, while Holmes kept a low profile, he did have friends.