Jeremy Richman, the father of a Sandy Hook school shooting victim, was found dead Monday morning from an apparent suicide, according to police in Newtown, Connecticut.
The body of Richman, 49, was found at Edmond Town Hall in Newtown, where his foundation had an office, authorities said.
If you are in crisis, please call the National Suicide Prevention Lifeline at 1-800-273-TALK (8255) or contact the Crisis Text Line by texting TALK to 741-741.
Richman's 6-year-old daughter, Avielle Richman, was among the 26 children and educators killed in the Dec. 14, 2012, mass shooting at Sandy Hook Elementary School.
Richman appeared last year on ABC News' "10% Happier" podcast, telling host Dan Harris that losing Avielle was "infinite heartbreak."
"She could light up a room with her smile, her giggle," he said.
Avielle had a strong sense of justice and was a "free spirit," Richman said. "She would narrate her whole morning in this ongoing song ... I really miss that."
"Fully understanding forever -- you will never see her again, you will never hold her ... that's with me in my mind always," he said, adding that over time "that feeling of sadness has definitely waned."
After his daughter's murder, Richman, a neuro-pharmacologist, founded The Avielle Foundation, a nonprofit "to study the neuroscience, the underpinnings of violence and the risk factors," he told "10% Happier."
"We wanted to prevent others from suffering the way that we were suffering," he said. "If there's a hope that we can get somebody help before it's another tragedy, then that would be everything."
"I suspect I would be bitter and frustrated and lacking a lot of purpose if I didn't do this," he said of the foundation.
"Jeremy was a good friend," Sen. Chris Murphy, D-Conn., told ABC News Monday. "He was someone so committed to understanding why these tragedies happen and why brains push people to acts of violence."
Murphy said Richman was at his office a few weeks ago and appeared "so excited about the work the foundation was doing and their ability to get their training program -- teaching about the way that the brain works and the way that it can fail to work properly -- to more and more people."
"It seemed like the future was limitless for the kind of work The Avielle Foundation could do," Murphy said.
“He knew that if we put more attention on the brain then maybe we can figure out how to identify somebody like [Sandy Hook shooter] Adam Lanza far before a tragedy happens," Murphy said. "I talked a lot to Jeremy about the stigma that exists, especially after these mass shootings, where folks think that everybody with mental illness must be prone to violence. And he really felt that research could help reduce that stigma.”
He continued, "Every single time somebody commits suicide you can't understand it. But in this case, Jeremy spent his entire life trying to help people identify the warning signs of harm. And it tells you how complicated the brain is, that even Jeremy couldn't figure out a way to get himself the help that he needed."
Police did not provide any additional details surrounding Richman's death beyond describing it as an apparent suicide. An autopsy is expected to be performed Monday, police said.
Richman and his wife, Jennifer Hensel, went on to have two more children -- a girl and a boy -- after Avielle's death.
"Our hearts are shattered and our heads are struggling to comprehend," The Avielle Foundation said in a statement. "Tragically, his death speaks to how insidious and formidable a challenge brain health can be and how critical it is for all of us to seek help for ourselves, our loved ones and anyone who we suspect may be in need."
"Jeremy’s mission will be carried on by the many who love him, including many who share the heartache and trauma that he has suffered since Dec.14, 2012," the statement continued. "We are crushed to pieces, but this important work will continue, because, as Jeremy would say, we have to."
Richman's death comes just days after what police say was the apparent suicides of two Parkland, Florida, area teenagers.
Connecticut Gov. Ned Lamont tweeted that he's "heartbroken for the Richman family."
"Thoughts and prayers just don't feel like enough in times like these," he wrote. "Words cannot even begin to express our sorrow."
Newtown Police Lt. Aaron Bahamonde called Richman's death a "heartbreaking event" for the Richman family and Newtown community.
ABC News' Ben Stein and Rachel Katz contributed to this report.