Francis Clifford Smith, believed to have been the longest-serving prisoner in United States history, has died at the age of 101 after spending decades in prison and having his execution postponed eight times.

Smith died in his sleep at a secure nursing facility for elderly people within the justice system.

He was 25 when he was sentenced to death for the 1949 murder of 68-year-old Grover Hart, a night watchman at a yacht club in Connecticut.

Hart was fatally shot on July 23, 1949, during an attempted robbery at the club. Smith was among two men arrested in connection with the killing.

Throughout his years in prison, Smith maintained his innocence despite his conviction and repeated efforts to overturn the death sentence.

His case became notable for the extraordinary length of time he spent behind bars and the repeated postponement of his scheduled execution.

Smith’s death at 101 brings to an end one of the longest and most controversial incarceration stories in US history.