(CNN) Soon after the December 2012 shooting at the Sandy Hook Elementary school in Connecticut, in which a gunman murdered 20 children and six adults, a question began to haunt the parents of 6-year-old Avielle Richman, one of the victims that day.
"I remember asking, 'Why would somebody walk into a school and kill my child?' " Jennifer Hensel told Anderson Cooper in 2013. "I need to know that answer. I have to have that answer."
To search for that answer, Hensel and her husband, Jeremy Richman, drew on their unique expertise. They were both scientists, and Richman was a neuroscientist long experienced in studying the human brain. Within days of the mass shooting, they set out on a mission to unravel the dark motivations inside the minds of violent offenders that trigger them to act.
It was the mission Richman devoted his life to, up until his death by suicide last week.
Richman had been tirelessly advocating, raising money and speaking up about the need for more brain research through the Avielle Foundation. Richman and his wife founded the organization to funnel money into brain science. Richman's vast knowledge and his ability to translate all of it for non-experts was why I called him in 2016 for a story about the criminal mind for CNN's sister network, HLN.
Richman diligently went through what we know and what we don't know about our behavior, translating complex neurological concepts and rattling off statistics about how much we spend globally containing violence. Richman was patient yet urgent.
"We need to really focus in on the science of the brain and feel comfortable talking about behavioral sciences," he said. "We need to make the invisible visible."
He was a public face for a growing group of people that includes researchers, law enforcement and those left behind by violent tragedies. Their pleas for more research were often overshadowed by the wave of talk about gun control, and they wanted to talk about more than mental illness.
Linking the study of violent behavior with those struggling with mental illness would only demonize a largely nonviolent group, explained Terrie Moffitt, a fellow neuroscientist who teaches at Duke University and is a friend of Richman's.
"He once told me that for eons, humans' survival has depended on bonding with others and trusting others," Moffitt wrote in an email. "The human brain is designed to love. So, if people suddenly become violent toward innocent fellow humans, there must be something fundamentally wrong inside their brain."
Doctors never say to a patient, "you are the flu" or "you are a broken bone." Yet Richman complained that when it comes to our mental state, we stamp the sufferer with the disease they have: "You're hyperactive." "You're bipolar." "You're depressed."
That label stigmatizes a person, and it can lead people to blame themselves when dangerous thoughts creep in. We accept that the stomach and the heart are real things, but we still consider the mind an abstract concept when, in fact, what's happening in the brain can have tangible origins, he explained.
"What we want to say is, our behaviors come from the brain," Richman said. "We need to move away from the sense of a character judgment or a flawed individual so that people are afraid to get help for themselves or for their loved ones."
The families of other school shooting victims have long echoed the same call. In 2015, I spoke to Joseph Samaha for the New York Times. He lost his daughter Reema in the Virginia Tech massacre in 2007 and was leading an initiative from the VTV Family Outreach Foundation to help staff on college campuses alert the right people when they noticed something wrong with a student's behavior. Teachers in that case became alarmed at the gunman's writing and alerted authorities, actions that didn't ultimately prevent the deaths of 33 people.
The warning signs surrounding the gunman's violent thoughts haunted Samaha and other parents long after the shooting.
"It's the science of it," Samaha said on the Virginia Tech campus in 2015. "It's the longer road. It's the seed we really have to plant."
Researchers called neurocriminologists have been studying the science behind antisocial, violent and criminal behavior for decades.
Adrian Raine, a professor at the University of Pennsylvania, wrote the book on violent minds and became a friend of Richman's. His findings over the past 40 years have been key in the field, and he is on the board of Richman's Avielle Foundation.
Much of Raine's work is based on looking directly at the brains of convicted criminals using brain scans. The technology Raine used has developed astronomically over the past decades, but its use is still not without skeptics.
Scans and other forms of biological research in the field have been illuminating. One of Raine's findings saw a correlation between criminal behavior and poor functioning in the front part of the brain, or the prefrontal cortex. Criminals he studied often exhibited poor planning and decision-making, lacking the ability to see consequences. Psychopaths, generally highly functioning, exhibited problems with the amygdala. That accounts for a serial killer's lack of remorse, because they have little ability to empathize with others in pain.
Criminology research also focuses on the limbic system. It regulates emotions like fear, hunger, anger and anxiety and is made up of the thalamus, the hippocampus and the amygdala. If the limbic system works properly together with that prefrontal cortex, it pushes us to act but also pulls us back if we're about to go too far. The limbic system builds a sort of memory of experiences that invoke feelings of guilt, shame and embarrassment.
We may get so angry that we want to do something about it, but we know intrinsically that might be the wrong choice. That's both a learned and a biological response.
Still, the overwhelming need to address the social factors behind violent behavior has taken center stage over addressing the biological part, Raine argues.
"I think the public are now much more aware than they used to be on the idea that brain differences, to some extent, shape individual differences in violence," Raine wrote in an email. "But how far that information can be used to prevent violence is a different issue."
Therapy is one established way to get people help when bad thoughts creep in. It's a behavioral science, and it helps address our environment and how we deal with it. That's the nurture part of the old adage "nature vs. nurture." That question tries to determine how much of a person's behavior is influenced by their biology or genetic makeup and how much by the people and stresses in their surroundings.
Both are important, experts agree. In fact, they affect each other. Abuse as children or stress at work can affect how we behave and how we feel, and so too can brain chemistry, according to research.
Researchers identified the chemical imbalances that correlate with problems such as depression, for example, and use treatments such as Prozac or Zoloft which block the reabsorption of serotonin so more of it can remain floating around in the brain. The more serotonin floating around, the happier we feel.
The problem, as neuroscientists see it, is that all the research we've done on what's going on inside the brain doesn't go far enough. Scientist Anthony Walsh spent two decades in law enforcement before switching to a career studying the impulses of the criminals he went after as an investigator. He's now a professor at Boise State University who, like others in his field, laments the lack of funding for research. More studies can help validate what criminologists are finding and help move toward prevention, he said.
"The brain is a tremendously complicated organ, and we know, perhaps, maybe, 10% of what we should know," Walsh said. "God almighty, all of this stuff taking place in a 3-pound little blob of Jell-O. It's just amazing."
Why does road rage cause some to flip a finger but others to go off the rails? Why does anger cause some to scream and shout but others to abuse and kill?
The Avielle Foundation has funded studies throughout the years at Duke University, the University of Northern Colorado and more. A study of twins it supported early on at the University of Michigan went on to receive a much larger grant from the National Institute of Mental Health. It compares identical and paternal twins to help figure out how antisocial behavior is affected by environment vs. genetics.
Richman and his colleagues from the foundation were also regulars on Capitol Hill and helped inform mental health reform legislation. He and foundation co-founder Ace Robinson sat next to then-Vice President Joe Biden when he announced an additional $100 million in funding for mental health services in 2013.
Robinson said the foundation's mission is to raise money for treatment and awareness but to also educate the public. He said Richman dealt with the tragedy of Sandy Hook by looking beyond the actions of that one individual who took his daughter's life. He wanted to address, instead, all the social and biological forces that pushed that gunman to act.
"Jeremy is someone who loved deeply and intensely," Robinson said. "You never heard the family talk about any particular mass murderer. They spoke about, 'What are the structures in place to make sure we understand what's happening and bring about change?' "
Richman believed that antisocial and violent impulses within might not be one person's "fault" but could be part biological, and understanding them would help people learn how much they really need help. And that would be a benefit to us all.
After Richman's death, a supporter and friend created a GoFundMe page to support the Avielle Foundation, Hensel and their two young children.
Hensel used the page to address supporters a few days after it went up: "The work of the Avielle Foundation is meaningful. But my champion and the love of my life is the person who had every tool in the toolbox at his disposal. He succumbed to the grief that he could not escape. Now we also honor Jeremy through the continued work of our foundation."
Richman hoped people understood more about the mind in every context, not just violence but loneliness, sadness and despair. While the number of school shootings continues to increase, so too does suicide.
Connecticut Sen. Chris Murphy sat in his office with Richman only two weeks before his death. They were trying to come up with ways to increase the scope of the foundation, because Richman was never satisfied that they were educating people enough about how nefarious the brain can be.
"It's Jeremy Richman who understood the brain and how it tries to trick you into violence, and he couldn't find a way to deal with the issues with which he struggled," Murphy said. "It speaks to how difficult it is for everyone else who's going through trauma."
In an interview with ABC Radio, Richman spoke about his daily struggles,. He said the time since his daughter's death was an "infinite heartache." But there was hope in helping. When asked what everyone else could do to help, Richman said, "having discussions about brain health, talking about your feelings and your motivations for doing things and recognizing that the brain is just another organ. ... That's really important. It's not a character flaw if you feel depressed."
"What struck me forcibly about Jeremy was his ability to look beyond personal tragedy and recognize that we desperately need to understand the causes of violence in order to prevent future tragedies," Raine wrote in an email. "That takes both enormous emotional courage as well as a clear-thinking, dispassionate mindset."