HALIFAX -- In the week since the mass shooting in Nova Scotia, a great many people have asked, what kind of a person could do such a thing, or why would a person do such a thing?

While we don't know much about the motives of Gabriel Wortman, we do know quite a bit about the risk factors associated with other mass shooters and multiple killers.

Dr. Rachael Collins, an assistant professor of criminology at Saint Mary's University, studies mass shootings and multiple murders. She said there hasn't been very much information published about Wortman to help provide any insight.

She said that, in general terms, researchers often find what she refers to as a "toxic seed."

"This is a large trauma in someone's life and this can actually begin to create a lot of anger," Dr. Collins said. "This starts a process of lifelong anger and they build a very toxic type of anger."

She said that this anger causes a lot of stress in the other people in the person's life and causes them to lose friends and partners because nobody wants to be around a very angry person.

Dr. Collins also identified another trait of mass shooters, what she referred to as "externalization of blame."

"They wind up blaming anyone and anything for their failure," Dr. Collins said. "This creates more anger and they see themselves as a victim."

Rage comes out of this, she said, and that is another key trait of mass killers.

"Rage is what we need to fuel an event like this," she said.

They also have issues with power and control and they tend to gravitate to something that is powerful or feels powerful, which is why they often pretend to be police officers or soldiers.