With another deadly shooting rampage in an educational institution, the question of 'why' arises.

In this case, we do not yet know the name of the 25-year-old gunman, who died at the scene from a police bullet (Update: He has now been identified as Kimveer Gill). Authorities have not said whether he was a student at Montreal's Dawson College, where the shooting rampage on Wednesday left a young woman dead and 19 others wounded.

However, the shooter has been described as a 25-year-old large Caucasian from the Greater Montreal area. Witnesses described a man dressed in black with a black Mohawk hairdo and a hard, menacing scowl on his face as he entered the school. His age would have made him older than the average student, as Dawson is a CEGEP school, a bridge between high school and university.

One theory about student school shootings is that they tend to be carried out by people described as misfits and loners who faced taunting and ostracization from their peers.

In Canada's two worst school shootings prior to Dawson, that label applied.

On Dec. 6, 1989, Marc Lepine killed 14 young women at Montreal's L'ecole Polytechnique before he killed himself. Lepine, the product of a reportedly abusive home, blamed "feminists" for all the problems in his failed life.

However, he wasn't a student at the school, although his application for admission had been rejected.

Just under a decade later -- and a week after the infamous shootings at Columbine High School in Littleton, Col. -- a 14-year-old entered W.R. Myers High School in Taber, Alta. and shot two people, leaving student dead.

That young man was described as bright but socially awkward, a victim of bullying who had left school as a result.

In 2004, a judge pronounced the young man displayed "psychopathic traits" and remained a danger to the public.

Peter Langman, director of psychology for KidsPeace, told CTV.ca there are three main types who commit school shootings:

• Those who come from abusive, dysfunctional backgrounds;
• Psychopaths;
• Those who are mentally ill and suffering from delusions, hallucinations or paranoia, to name a few symptoms.

Unfortunately, what experts don't know is why someone in one of those groups will explode and harm others, he said.

Jean Twenge, a psychology professor from San Diego State University, told CTV.ca that in the majority of school shootings, social rejection was a factor.

This factor also exists in workplace shootings and many domestic incidents, she said.

"It's almost always an employee who got fired," she said, adding, "A fair bit of domestic violence occurs when the woman says, 'OK, we're breaking up, I really mean it this time.' That thread runs through a lot of violence."

Montreal has had a workplace-type shooting in an academic institution. In 1992, Dr. Valery Fabrikant killed four of his Concordia University colleagues and wounded another. He blamed some of them for his not getting tenure and had other complaints about them.

In adolescent shootings, however, Langman said there is almost always "leakage" of the shooter's plans.

Take these words from Cody Thunder, wounded in the shooting spree of Jeff Weise at the Red Lake Indian Reserve in Minnesota in March 2005. Nine people died, including Weise. Before that terrible day, Thunder tried reaching out to Weise, who appeared to have no friends: "He looked like a cool guy, and then I talked to him a few times. He talked about guns and shooting people."

"Most of these are committed by people who are, relatively speaking, sane, but who have this deep-seated anger. So they try to get the attention of the people around them, and when that doesn't work, they just do it," Twenge said.

While rejection is one factor, narcissists, "people who are just very, very full of themselves," can also blow up when they feel wronged, she said.

That runs counter to the notion that some of these attackers suffer from low self-esteem, she said.

Other influencing factors on aggression include playing violent video games and "frankly, the availability of guns, which is why we have more of these in the United States than you do in Canada, because you have better gun control," Twenge said.

Langman said school shootings gain a huge amount of media attention when they occur, but people should remember school remains the one of the safest places for young people.

In terms of prevention, Michael Hoechsmann, a professor of counselling and educational psychology at Montreal's McGill University, told CTV's Newsnet that society does not listen enough to young people.

"When you find a young person with a gun in their hand, you're more likely to listen to them than when they have a pencil or are sitting at a computer terminal."

Stereotyping of the person through clothing -- "the mohawk, the piercings" -- stand in for any understanding of the young person, he said.

In no other crime scene would people discuss clothing before motive, "so we might have something to think about there," Hoechsmann said.