AUSTIN (KXAN) — What drives a person to kill on a widespread level?

The National Institute of Justice wants to know, and is helping to fund The Violence Project, a nonpartisan think tank hoping to reduce violence in America.

It’s studied all 163 mass shootings where four or more people died in the U.S. since 1966, starting that year with the University of Texas Tower shooting.

“What we do have are these common themes that run throughout each and every one of these shootings,” said James Densley, the project’s founder.

Through interviews with mass shooters in prison, their family members, law enforcement, and victims, Densley’s identified four repeating similarities the shooters share.

The first is a troubled or traumatic childhood.

“They’ve experienced trauma, abuse, and are living in very, sort of difficult circumstances,” Densley said. “We’re talking about the suicides of parents, we’re talking about neglect and abuse within the household.”

Next, the person reaches a crisis point where they no longer feel like living.

Densley said many of the shooters are suicidal and turn homicidal.

“They’re often searching for answers to make sense of their life some way, to give it meaning,” he said.

• WATCH: James Denley’s Ted Talk on the traits of mass shooters

Third, research shows most shooters seek to validate the violence they’re contemplating.

They’re fascinated by other mass shooters and study them. Mass shooters are also often captivated by the notoriety social media and the 24-hour news cycle can offer.

“In the darkest corners of the internet you can find anyone and everyone who will agree with your viewpoint and sort of validate your thinking, make your grievance seem like it’s legitimate,” Denley said. “This can create almost like a radicalization process where people start to believe that a mass shooting is a viable solution to their problems.”

• READ MORE: Do video games cause violence? Here’s what the research says

The last piece of the puzzle is accessibility — to places, people and guns.

Densley found in 80 percent of school shootings, perpetrators got their weapons from family members.

In other public shootings, most shooters got their guns legally.

“In the end, if you can’t procure the guns, you can’t get the weapons, then you can’t perpetrate the shooting,” Densley said.

Densley’s research leads him to believe there is no one size fits all solution.

He said society should start by training more schools and workplaces in crisis intervention, suicide awareness, de-escalation.

From there, he said it’s important to address each of the four focuses individually.

“You can intervene in early childhood, you can intervene at the point of the crisis itself, you can intervene in the way of which we spread the message of hate,” Densley said. “We can also do things to prevent vulnerable individuals from getting access to firearms.”