Alienated and disturbed young men like Elliot Rodger who go on shooting sprees are often modelling their behaviour on other male violence, experts say, and choose mass killing "as the mark with which they can be men."

Dr. Michael Welner, a New York based forensic psychiatrist whose cases have included mass killers who survive their rampages, says the fact that perpetrators of mass killing are male underscores it as a social phenomenon.

"Maleness in contemporary culture is increasingly defined by icons whose destructiveness is their masculinity," Welner said in an email. "There is nothing in feminine role modelling that underlines large-scale destructiveness, and so women don’t model this behaviour."

Friday night's rampage near the University of California, Santa Barbara, left six victims dead and 13 injured. Rodger, who died of an apparent self-inflicted gunshot, had left a trail of YouTube videos and a 140-page manifesto ranting against women and couples and lamenting his lack of a sex life.

California shootings George Chen

A note addressed to George Chen, 20, of San Jose, Calif., one of three men found stabbed to death in the apartment of Elliott Rodger, outside the apartment where he lived in the Isla Vista neighborhood of Goleta, Calif. (Christopher Weber/AP)

Welner said that young people can tap into "destructive fantasy" at a time when they are learning to be men, formulating their identity and how they express themselves as men.

"Some of those who are alienated and with high expectations of themselves, and entitlement, and propensity to blame others in broader society, degenerate to the end that they choose mass killing as the mark with which they can be men."

James Garbarino, a psychology professor at Loyola University Chicago, said that when people do "crazy" things, they always do it in a particular cultural framework and context. Dramatic violence has not been part of the cultural landscape for girls the way it is for boys, he said, although there has been some shift.

“When a boy is in this state, he has all of these scenarios to play out," Garbarino said.

'It's a boys' thing to do'

Garbarino, who has written the forthcoming book I Listen to Killers: Lessons Learned from 20 Years as a Psychological Expert Witness in Murder Cases, said he interviewed an 18-year-old who showed up at school with two guns and a bagful of bombs. The boy, who was intercepted before he could cause any harm, said he had studied the Columbine school massacre as if it were a primer.

"So there is that element and it sort of builds momentum. Boys do it and other boys see it and it’s a boys' thing to do."

While there's an element of "copycat" behaviour, culture plays a role in how one acts out violently, he said.

"You might do something different if you were in the same mental state as [Rodger] if you lived in Pakistan or if you lived in Nairobi or if you lived in Sweden. There's always that element of cultural script or scenario that's important and why one crazy 22-year-old does this and why another does something else."

Another common cultural factor in these types of rampage or school shootings is that the gunman is usually white, Garbarino said. 

"These are very highly, highly vulnerable individual kids. When they live in middle-class, upper middle class educated families, families have the resources and the capacity to sort of buffer them from the world. And provide them a high level of support," Garbarino said.

"If a kid like this was born in a poor black or Hispanic gang-ridden neighbourhood, he wouldn’t get this far before his vulnerability translated into violence," he said. "You would see it in first grade or second grade because the mismatch between their vulnerability and the level of stress and oppression and lack of resources would bring it out."

Garbarino said disturbed youth also have access to social media to validate their beliefs.

"Back before all this, if you were a weird kid, you mostly got back social feedback that said you were weird. Today there’s virtually no weird thought that you can't find validation for when you get on the web. All killers feel they’re justified in what they do. The fact that you can post stuff and other people will say 'Yeah, I know what you mean '—  this comes as a validation from the media."

Rodger, like Norway’s mass-shooter Anders Breivik and former LAPD officer Christopher Dorner who killed four people, all used social media to move around the traditional press and to directly communicate their packaged propaganda, Welner added.

With files from The Associated Press