Frank Smith, who served 70 years in prison — one of the longest known terms of incarceration in American history — for fatally shooting a Connecticut yacht club’s night watchman during a robbery in 1949, died on June 25 in Rocky Hill, Conn. He was 101.

His death, at a nursing home to which he had been paroled, was confirmed by the Connecticut Department of Correction and was previously reported by The Boston Globe and Greenwich Time.

In 1950, Mr. Smith was convicted of the first-degree murder of the watchman, 68-year-old Grover Hart, and sentenced to death. Mr. Smith, who insisted on his innocence, eventually received eight reprieves from the electric chair in Wethersfield, Conn.

His case attracted the attention of Aaron Cohen, a realtor in West Hartford and a member of the American League to Abolish the Death Penalty. Mr. Cohen visited Mr. Smith and orchestrated a telegram- and letter-writing campaign to stop the execution.

“I did not believe all Smith told me at first, and it took me time to believe him,” Mr. Cohen told The Hartford Courant in 1951, adding: “I am convinced that an innocent man is going to his death. He has already died too many times in his cell.”

In 1954, on the eve of Mr. Smith’s last scheduled execution, a Courant reporter wrote that he “spends most of his time trying to figure out how he was convicted. He discusses his case with anyone who’ll listen.”

The article described how, before a planned execution a year earlier, a chaplain had visited Mr. Smith in his cell. “All he wanted to talk about was his trial,” the chaplain recalled.

On June 7, 1954, two hours before he was to be strapped into the chair, the state’s Board of Pardons and Paroles commuted his death sentence.

“Thanks be to God!” Mr. Smith said in the hearing room, where his parents, three sisters and two brothers were watching.

Seven decades later, he remained haunted by the electric chair — “still an object of primal, almost talismanic fear,” Annalisa Quinn wrote in a 2023 profile in The Boston Globe Magazine. “‘It cooks you,’ he would repeat, folding into himself. ‘It cooks you.’”

In 2012, Connecticut outlawed the death penalty.

Except for a brief escape attempt in 1967 and nearly 10 months on parole (which he violated) in 1975, Mr. Smith remained in prison until 2020. The state then paroled him to 60 West, a private facility that helps the state care for formerly incarcerated people who are difficult to place in traditional nursing homes. There, he lived in a secure unit.

A spokesman for the correction department said Mr. Smith’s six years at 60 West meant that he had served 76 years of his life sentence.

It is not known if that is officially America’s longest imprisonment. “Seventy years is a long time,” Paul Wright, the editor of Prison Legal News, wrote in an email, “but I think there are probably some more out there just because the U.S. locks up so many people and also locks them up for such long periods of time.”

Francis Clifford Smith was born on Sept. 1, 1924, in Stamford, Conn., and at some point moved to the Noroton neighborhood of nearby Darien. His mother was Doris (Curtis) Smith, and his father, also named Francis, was a roofer, according to The Globe, which reported that Frank was sent to a reform school when he was 10 or 11.

He then served time as a teenager in a reformatory for young men and, after escaping and assaulting a guard with a deadly weapon, was sent to a state prison for four years. He later worked as a messenger for a numbers racketeer.

On the night of July 23, 1949, two men broke into and burglarized the Indian Harbor Yacht Club in Greenwich. By some accounts, Mr. Hart surprised them, and one or both of the robbers shot him.

Before he died, Mr. Hart told police that one of the men wore a bandanna; Mr. Smith was known to police for wearing one. After a manhunt, he was arrested in the woods in Wilton, Conn. George Lowden, his accused accomplice, was also arrested.

Mr. Lowden struck a plea deal for second-degree murder, and he implicated Mr. Smith. During the trial, Mr. Smith denied his involvement in the crime, and his father testified that he found his son asleep in his car on the night of the shooting.

The jury’s verdict against Mr. Smith was clouded by several factors, including Mr. Lowden’s refusal to testify at the trial. Then, two years after the trial, a witness recanted testimony that had suggested Mr. Smith’s culpability.

In 1953, David Blumetti, an armed robber from Stamford who was imprisoned in Alabama, confessed to the murder and said that he and Mr. Lowden had been partners in the crime.

Mr. Blumetti said that he knew Mr. Smith from a previous prison stint. He said that the two men met earlier on the day of the robbery and murder, drove around in Mr. Smith’s gray Cadillac and discussed places they could rob. By Mr. Blumetti’s account, Mr. Smith decided against the robbery, and Mr. Blumetti said that he borrowed Mr. Smith’s car, picked up Mr. Lowden and, with Mr. Lowden, fired at Mr. Hart.

“They’ll be executing the wrong man,” Mr. Blumetti told The Connecticut Post in the days before the state pardons board met to commute Mr. Smith’s death sentence.

At that hearing, Leo F. Carroll, the state police major who had interrogated Mr. Smith after his arrest, told the panel that he believed Mr. Blumetti’s confession and that Mr. Smith was innocent.

“I’m positive he didn’t kill Grover Hart,” Mr. Carroll said. “I’m not even sure he was present at the murder.” Pleading for Mr. Smith’s life, Mr. Carroll said, “In the name of Him who we must all someday ask for mercy, I beg each of you to have mercy in this case and permit Frank Smith to live.”

Mr. Smith never got a new trial, and he was never exonerated. In 1964, he sought his freedom when he filed a 259-page petition for a writ of habeas corpus — a legal challenge of improper detention — that contained 221 instances of what he said were his constitutional rights having been violated. The U.S. Court of Appeals for the Second Circuit rejected it.

In 1967, Mr. Smith was being held in the minimum-security division of a state prison in Enfield, Conn., and working as an auto mechanic when he stole a truck and escaped for 12 days. After a manhunt, he was arrested in Winthrop, Mass.

He was paroled in early 1975 but returned to prison late that year after being arrested for larceny and possession of dangerous weapons.

Not much was heard from him after that. He was in his late 90s by the time Ms. Quinn of The Globe, who was interested in how decades of incarceration affect people, began visiting him in the nursing home in 2022. She wrote that he was so small that she could have easily picked him up.

“Even now, Smith seems to live perpetually in the time of his trial,” she wrote. “He has mild dementia, and doesn’t always recall what he did a day ago. But he remembers his public defenders, members of the jury, who said what and when. He can’t stop replaying these details for anyone who will listen.”