Doing so means diverting critical attention from the real objective --spotting telltale behaviour in an individual about to perpetrate a bloodbath, said Steve Albrecht in a telephone interview.

"We're all shocked (but) it certainly doesn't make people feel any better to know what the motive is," said Albrecht, who heads the San Diego branch of the Association of Threat Assessment Professionals.

"I'd want to working on interrupting the opportunity (to commit a mass murder), to stop these guys when they exhibit those (suspicious or worrisome) behaviours early on."

James Holmes, 24, is suspected of donning a mask and body armour, then opening fire during a midnight showing of the latest Batman movie in Aurora, Colorado, killing at least 12 people and wounding nearly 60 others.

The bloodbath shocked Americans, even though the United States sees about 20 mass murders -- defined as three or more deaths at the hands of a single perpetrator in a single uninterrupted incident -- every year.

Albrecht, a former police officer in Holmes' hometown San Diego who holds psychology and business degrees, is co-author of "Ticking Bombs: Defusing Violence in the Workplace" and advises businesses on threat assessment.

Speaking to AFP within 24 hours of Friday's tragedy, Albrecht speculated that the Colorado gunman -- who has yet to appear in court -- was likely a "serial loser" in search of infamy.

Many troubled people never get beyond fantasising about committing an act of violence, but "here's a guy whose probably ruminated over this for weeks and months and moved from ideas to action," he said.

"It was a lot of pre-attack preparation for a guy who's hard to notice because he's not part of an organized group or on a terror watch list. It's very difficult to stop these people."

Albrecht added: "I suspect we're going to discover that the guy had a lot of issues that he chose to solve through this method" of raking a midnight movie audience with gunfire.

Prior to the Columbine high school massacre, in which two students cut down 12 students and a teacher in 1999 before killing themselves, law enforcement agencies concentrated on building profiles of mass killers, Albrecht explained.

But as it emerged that anyone of any age, race, gender or socio-economic background could and did commit mass murder, the focus swung towards picking out acts of behavior that would reveal a solitary killer in the making.

"Now we're really looking at behavior and moving away from profiling," he said, recalling how a 1998 rampage in an Arkansas school in which five died had been carried out by two boys aged just 13 and 11.

Typical questions to ask: "What were the pre-attack behaviors that this guy exhibited? What were the relationship failures, relationship problems that he had? Was he disconnected from society and disconnected from reality?"

Elaborating on an essay he wrote on the topic for Psychology Today magazine, Albrecht said people "tend to rationalize the irrational behavior of the people around us" and thus skip over signs of an individual on the verge of violence.

"My suspicion is that they're going to learn a lot of things (about the Aurora gunman), and that people were very concerned about this guy -- but didn't know what to do."