Oscar Franklin Smith, 72, the oldest inmate on the state’s death row, is scheduled to die by lethal injection at the Riverbend Maximum Security Institution in Nashville this evening.

He was convicted of fatally stabbing and shooting his estranged wife Judith Smith, 35, and her sons, 13-year-old Jason Burnett and 16-year-old Chad Burnett, at their Nashville home in October 1989.

Smith’s attorneys had asked Republican Gov. Bill Lee for clemency. But Lee issued a brief statement on Tuesday, saying he would not block the execution.

“After thorough consideration of Oscar Smith’s request for clemency and an extensive review of the case, the State of Tennessee’s sentence will stand, and I will not be intervening,” Lee said.

Smith has maintained that he is innocent.

The state Court of Criminal Appeals last week denied Smith’s request to reopen his case after an unknown person’s DNA was found on one of the murder weapons.

Smith “has not presented new scientific evidence establishing that he is actually innocent of the murders of the victims,” the ruling said, according to The Tennessean.

The Tennessee Supreme Court on Monday declined to hear his appeal.

Smith’s attorney Amy Harwell said the state has built a “roadblock” to Smith’s claims of innocence.

“Mr. Smith has maintained his innocence for more than thirty years. New cutting-edge DNA evidence excluding Mr. Smith as the contributor of DNA evidence on the murder weapon in this case proves his claim,” Harwell said in a statement to Newsweek.

“The state has erected an insurmountable roadblock to Mr. Smith’s claims of innocence. The Governor’s denial of clemency under these circumstances is extremely disappointing.”