One gunshot.

Then another.

Within minutes, a prominent death-with-dignity advocate was shot dead along with his ailing wife in an assisted living center in Florida.

Eighty-one-year-old Frank Kavanaugh — who served on the national advisory board for the Final Exit Network, an advocacy organization in the right-to-die debate — was discovered dead in the early morning hours Tuesday alongside his wife, 88-year-old Barbara Kavanaugh.

The couple was found at the Solaris HealthCare Charlotte Harbor center in Port Charlotte, Fla. Charlotte County Sheriff’s Office spokesman Skip Conroy said the case is being investigated as a murder-suicide.

But those who knew the Kavanaughs said it may have been their only option.

“It was a rational suicide,” Final Exit Network President Janis Landis told The Washington Post. “Both of them made this decision. It was not murder.”

Frank Kavanaugh. (Courtesy of Final Exit Network) Frank Kavanaugh (Courtesy of Final Exit Network)

Fellow members of the Final Exit Network said Kavanaugh had recently pulled away from his own life to stay by his wife’s side as she battled a degenerative brain disease.

“He had really disengaged from everything else,” Landis said. “He was at her side every day, all day. He hadn’t spent a night away from home since she got the diagnosis.”

Landis, the group’s president, said several members knew what the Kavanaughs had been going through but none knew how bad it had gotten.

“We’re not surprised that both of them felt strongly about their right to decide the timing and manner of their deaths when the quality of their lives became unacceptable,” she said.

Landis noted that, as far as she knew, no one was aware of the couple’s plan.

According to Florida law, assisted suicide is manslaughter, a second-degree felony.

Authorities have not yet released a possible motive in the Kavanaughs’ case.

Just after 1 a.m. Tuesday, authorities were called to the Solaris HealthCare Charlotte Harbor center, where they found the couple. Both had been shot and killed.

“We would like to express our sincere condolences to the family of the husband and wife involved in a tragic event that occurred at our facility last night,” F. Stan Weye, an administrator for Solaris Healthcare, told ABC affiliate WZVN in a statement.

After the couple’s deaths, friends, neighbors and fellow right-to-die advocates started to speak out about the violent and heart-wrenching scene.

Robert Rivas, general counsel for the Final Exit Network, called Frank Kavanaugh “one of the best, most beloved and dedicated” members of the group and wrote on Facebook that “the Sheriff’s Office labeled the deaths of Frank and his wife, Barbara, a ‘murder-suicide,’ but I would call it the tragic consequence of living in a country that prohibits people from exercising any type of informed choices in death.”

People in the pair’s Punta Gorda community depicted a heartbreaking image of an elderly husband who was desperate to help the love of his life.

“He was in good shape, good health; I can’t imagine why this horrible thing happened,” Gale Petrillo told WZVN. “I’m stunned. It’s horrific. Sometimes we could hear him say, ‘Barbara, but I’m only trying to help. I’m only trying to help.’ ”

But another friend, Ted Goodwin, said Kavanaugh had started having health issues, which, Goodwin thought, may have led to a deadly decision.

“They were with each other constantly over a lifetime,” he told the news station. “My guess is they had determined to go together. While my heart is breaking on one hand, I have to honor the fact they went on their terms.”

Frank Kavanaugh was retired after a long teaching career at the George Washington University School of Medicine, according to his Final Exit Network biography. The school, however, could not immediately verify his employment history.

In a 2014 interview, Kavanaugh said his time in the field had allowed him to see not only how modern medicine helped people but also how it hindered them near the ends of their lives.

“With my 23 years in the medical center, I saw the wonderful things that we did in intervening in people’s lives and making them better — and, unfortunately, I also saw how when we could not make them any better we too often walked away from them at the most critical time in their lives,” he said in 2014, adding that he didn’t think the medical profession was responding in the right way.

“Lots of emphasis on keeping people alive; not enough on what we could call ‘end-of-life care’ or really ‘aid-in-dying.’ ”

In recent years, there has been an emotional push from right-to-die advocates such as Kavanaugh to urge states to adopt laws that would allow terminally ill patients to choose how they want to go.

In late 2014, Brittany Maynard — a vibrant 20-something who was losing her fight against brain cancer — became a major figure in the right-to-die debate when she announced that she had planned her own death.

Maynard moved from her home in California to Oregon, one of now five states that permits physician-assisted suicide under its Death with Dignity Act.

Before Maynard’s death, a 2013 poll conducted by the New England Journal of Medicine showed that 67 percent of more than 1,700 people surveyed in the United States were against physician-assisted suicide.

That same year, a Pew Research survey showed that public opinion was split, with 47 percent of U.S. adults supporting the practice and 49 percent opposing it. A Gallup poll that year suggested that results varied according to how the question was presented: Some 70 percent of Americans were in favor of allowing physicians to “end the patient’s life by some painless means,” but only 51 percent were in support of allowing doctors to help a patient “commit suicide.”

Since then, some things have started to change.

Last year, California Gov. Jerry Brown (D) signed a measure to legalize physician-assisted suicide in the state.

A poll at the time showed a 10-point rise in support from 2014 — an increase “consistent with changing attitudes related to a number of once-controversial social issues,” according to Gallup.

But not everyone agrees with doctor-assisted suicide — and some opponents have made their opinions known.

Amid the debate in California, Stephanie Packer, who has been battling her own terminal illness, said she worried that the option to die would prevent people from trying to find a way to live.

If assisted suicide is an option, she told The Post’s Niraj Chokshi last year, it will be “easier to give in to that all-consuming feeling when you find out that your life is closing.”

The American Medical Association, it seems, agrees.

“Instead of participating in assisted suicide, physicians must aggressively respond to the needs of patients at the end of life,” the organization said in its opinion on physician-assisted suicide. “Patients should not be abandoned once it is determined that cure is impossible.”

The deaths in Florida this week have already prompted further discussion about the death-with-dignity debate.

Landis, the Final Exit Network president, drew parallels between the Kavanaughs’ deaths and a time before abortion was legal, when some women would use coat hangers to perform their own procedures.

“In an ideal word,” she said, “people would not have to resort to such violent means.”

Correction: A previous version of this post incorrectly characterized the findings of a New England Journal of Medicine poll. The post has been updated.

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