His daughter, Avielle Richman, was one of the 20 first-grade students and six educators killed in the 2012 massacre.
Police confirmed the father had died on Monday morning, declining to provide any other details except that his death did not appear suspicious.
“This is a heart breaking event for the Richman family and the Newtown Community as a whole, the police department’s prayers are with the Richman family right now, and we ask that the family be given privacy in this most difficult time,” Newton Police Lieutenant Aaron Bahamonde said in a statement.
The father was found by an electrician at Edmond Town Hall early Monday morning, according to police. The chief medical examiner will determine the official cause of his death.
The Richman family created the Avielle Foundation after the mass shooting to promote “brain science research” that probes murderous and other violent actions committed by individuals like the man who stormed their daughter’s elementary school six years ago.
The Avielle Foundation has an office located inside the Edmond Town Hall.
Mr Richman became a prominent supporter of mental health care reform following the shooting, telling lawmakers in a January 2013 hearing, “We must act to ensure this doesn’t happen again.”
He reportedly left his job at the Boehringer Ingelheim pharmaceutical company, where he worked as a researcher, in order to spend more time working at the foundation.
Two survivors of another school shooting in Parkland, Florida also died from apparent suicides within the past week.
“My heart breaks for this family, which has already endured so much,” Senator Richard Blumenthal said in a statement. “This is a gut punch. I came to know his family after Sandy Hook, I attended the funeral. My prayers go out to them.”
He added, “The cascading harm done by that savage, unspeakable act reminds us of the trauma that’s caused – and the after-effects.”
If you are in crisis, call the National Suicide Prevention Lifeline at 1-800-273-TALK (8255), or contact the Crisis Text Line by texting TALK to 741741.