An 81-year-old inmate who was the “longest serving resident of South Carolina’s Death Row” died of natural causes this week, officials said. 

The South Carolina Department of Corrections reported on Friday that Fred Singleton died on Monday at Kirkland Correctional Institution’s infirmary. In 1983, Singleton was sentenced to death for the rape and strangulation of a woman in Newberry County, as well as stealing her jewelry, according to court documents.

Singleton remained in a legal standstill for over thirty years after the state Supreme Court declared he was not mentally fit for execution. Singleton couldn’t comprehend the possibility of his death by electric chair and would respond to his lawyers’ questions solely with “yes” or “no,” The Associated Press reported.

Nevertheless, in 1993, the justices decided that while Singleton’s death penalty should be maintained in the event of future psychological improvements, he shouldn’t be medicated purely to make him competent for execution, per the AP.

There are now 24 men remaining on South Carolina’s death row after Singleton’s death.

There have been two firing squad executions in South Carolina this year. 

In early March, 67-year-old Brad Sigmon, who had been convicted for the murder of his ex-girlfriend’s parents in 2001, became the first person in fifteen years to be executed by firing squad in the United States.

The following month, Mikal Mahdi, 42, was put to death by the same method. He was convicted in the 2004 killings of an off-duty police officer in Calhoun County in South Carolina and a convenience store clerk in Winston-Salem, North Carolina. He was sentenced to death for the murder of the officer and to life in prison for the clerk’s murder.