Unlike most of America who woke up last Sunday stunned to hear the news of a mass shooting in Dayton, Ohio just hours after the devastating carnage in El Paso, Texas, Lori Post wasn’t surprised. The Northwestern University epidemiologist and sociologist studies violence, with a focus on the motivations of mass shooters.

Post's research shows that the days between what she calls “massacres” have been steadily decreasing over the past few decades. In a grim support of her data, the Dayton and El Paso mass killings were the third in a week, following the shooting at the Gilroy Garlic Festival, which left two children and an adult dead.

“It was just a matter of time for two to hit the same day,” she told NBC News.

Post's work is part of a growing field science to discover predictive risk factors for mass killings and consider a range of solutions, including those from the arenas of medicine and public health. Psychologist Jillian Peterson, one of the founders of the Violence Project, a nonpartisan think tank, has created a database of mass shooters from 1966 to 2018 to look for trends and patterns.

With President Donald Trump and Washington lawmakers expressing support for new gun control measures, including "red flag laws" to allow courts and police to confiscate firearms from people believed to be a threat to themselves or others, Peterson’s research has identified several key characteristics common among most mass shooters.

A potent predictor Peterson’s database has revealed is suicide: the shooters are almost always suicidal. Her latest analysis shows that 80 percent of the perpetrators were suicidal before the shooting, which she says it is key to understanding their actions.

“In every case, this was intended to be their final act,” said Peterson, a professor of criminal justice at Hamline University in Minnesota. “They are murders, but they are murder-suicides. Meaning, the perpetrator doesn't intend to make it through the shooting — they are either killed by police, they shoot themselves, or they spend the rest of their lives behind bars.”

One critical pathway to stop future massacres could be to focus on suicide prevention, Peterson believes.

“We know more about the field of suicide prevention in terms of what works, and those same strategies might be effective here,” she said.

Other commonalities Peterson’s research has found among mass shooters include childhood trauma, domestic violence, or a parent’s suicide. A crisis point, such as being bullied or fired from a job, usually precedes a shooting rampage.

“Something happens where they go into a tailspin and become actively suicidal,” Peterson said.

Her research finds the shooters almost always find ways to validate their feelings of anger or aggression, often joining online hate groups with others who share the same emotions.

Finally, the research shows the shooters all had access to a gun. The Northwestern team found that 81 percent of mass shooters used semi-automatic weapons, military-style weapons and large cartridges with a big kill capacity.

“At every opportunity, we need to make it a point to stop it,” Post said.

If you or someone you know is in crisis, call the National Suicide Prevention Lifeline at 800-273-8255, text HOME to 741741 or visit SpeakingOfSuicide.com/resources for additional resources.

Follow NBC HEALTH on Twitter & Facebook.