Federal law enforcement agencies have joined in the search for a Massachusetts woman known for her work raising awareness about suicide among police officers and who is now a suspect in the death of her police officer husband.

Thursday marked the third day of a hunt for Karen Solomon after Worcester police responded to the couple’s Wildwood Avenue home at about 5:28 a.m. Tuesday for a report of a person down and found her husband, off-duty Worcester police officer Kurt Solomon, dead.

For years, Karen Solomon has been an influential advocate for the mental health of police officers and their families. She co-founded First H.E.L.P., an organization focused on suicide prevention and mental health among first responders, and wrote two books about the toll police work can take on officers.

Her advocacy also brought her before a federal law enforcement commission. In 2020, Solomon participated at a Justice Department hearing of the President’s Commission on Law Enforcement and the Administration of Justice, where she testified on a panel devoted to support for officers and their families.

First H.E.L.P. acknowledged the death Tuesday, saying its “first concern is for the officer who lost his life, his family, his colleagues, and the Worcester law-enforcement community.”

“We extend our deepest condolences to all those affected by this tragedy,” the organization said, adding that its mission to support first responders and their families remains unchanged.

Police Chief Paul B. Saucier said Karen Solomon should be considered armed and dangerous. Several law enforcement agencies have been assisting in the search, including the Massachusetts State Police, Homeland Security Investigations and the U.S. Marshals Service.

Police described the death as “an act of domestic violence” but have not said how Kurt Solomon died. Worcester District Attorney Joseph Early Jr. said officials were limited in what they could disclose because of state laws protecting information about domestic violence victims.

“She’s a suspect with regards to this case. We want her for questioning,” he said at the news conference. “She was at the house. We’d be able to ask her with regards to what happened at the house, what went on at the house.”

On Wednesday, police released security video showing Karen Solomon walking down the street wearing shorts, a T-shirt and flip-flops.

“We ask the public to remain vigilant,” the department wrote on Facebook.

Dan Wilson, who has lived across the street from the Solomons for 13 years, said he was “shocked” by what happened.

“You don’t see it coming,” he said in a phone call on Thursday. “It all feels very surreal.”

Wilson said he would occasionally talk to Karen Solomon about things happening on their street and remembered the couple as “very kind people.”

Gabrielle Wilson said she’d talk to Karen Solomon in a community Facebook group about “potholes and neighbors, or she’d come over and chat about our gardens.”

She described the family as quiet.

“It never crossed my mind that there may be something going on at home that would cause this tragedy,” she said.

Kurt Solomon worked as a patrol officer with the Worcester Police Department for over 30 years. The New England Police Benevolent Association said he was known as an “incredibly dependable officer, colleague and friend.”

“His loss is being felt deeply throughout the Worcester Police Department, NEPBA Local 911 and our entire Association,” NEPBA said in a Facebook statement.

Union President Thomas Duffy II said at a news conference that Kurt Solomon was getting close to retirement.

“He’s a tremendous person and tremendous police officer,” Duffy said. “It’s a very difficult time.”

Karen Solomon’s work on police mental health included two books: “Hearts Beneath the Badge,” which focuses on the experiences of law enforcement and their families, and “The Price They Pay,” about the physical and emotional effects of traumatic events on officers. She also wrote several articles on law enforcement suicide, according to a biography on First H.E.L.P.

In articles published by Police1, a website intended for law enforcement, she wrote about police families, officer wellness and efforts to track and prevent suicides among current and former officers.

Her work also gave her a public profile. A DOJ biography says she was the co-chair of the data and research committee of the National Consortium on Law Enforcement Suicide Prevention and spoke at government events about law enforcement suicide. MassLive.com reported that she appeared on at least six talk shows, podcasts and media programs, including a 2020 appearance on “Dr. Phil.”