ST. PAUL, Minn. (AP) — Minnesota researchers have created a new database that seeks to help understand circumstances that contribute to mass shootings in the United States.

The nonpartisan Violence Project’s database went online Tuesday, Minnesota Public Radio News reported. The project’s researchers chronicled traits related to 171 people who committed mass shootings, which are defined as shooting and killing four or more people in a public space.

James Densley, co-founder of the Violence Project and a criminal justice professor at Metropolitan State University, said researchers looked at factors in the lives of shooters, including mental health troubles, whether they considered suicide, and how they had access to guns.

"For a start, we need to be a little bit more attuned to the fact that people are in crisis, and are looking for help, and perhaps aren't getting it," Densley said.

Researchers found that 98% of mass shooters were men and that 52% were white. The proportion of mass shooters who had been diagnosed with mental health conditions was only marginally higher than the overall population, according to researchers.

About 77% of mass shooters purchased some of their firearms legally. Almost half the shooters leaked their plans ahead of time. One-fifth of them studied other mass shooting incidents.

Mass shootings have claimed more than 1,200 lives in the last half century, the researchers found. Densley noted that the number of shootings and number of victims has progressively increased.

"We're just fed up with switching on the news and hearing about another mass shooting in our community and another community that's shattered by that,” Densley said. “I think it’s time to move into action.”

Jillian Peterson, another co-founder of the project and an assistant professor of criminology and criminal justice at Hamline University in St. Paul, said the database might inform policies that could avert future mass shooting incidents.

“Mass shootings are a complex issue, requiring multiple avenues of prevention,” Peterson said in a statement. “The goal of this project is to ground our public policy discussions in data and develop evidence-based policies to prevent these tragedies.”

The database was established with the support of the National Institute of Justice.

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Information from: Minnesota Public Radio News, http://www.mprnews.org