Three weeks before he was executed for killing his estranged wife, authorities say, a death row inmate in Mississippi revealed the location of the body of his sister-in-law, who disappeared in 2007.

Attorneys for the man, David Neal Cox, told prosecutors about the purported confession of his involvement in a second homicide in “hand-delivered writings” on Nov. 19, First Circuit District Attorney John Weddle said in a statement.

The notes were provided two days after he was killed by lethal injection at the Mississippi State Penitentiary at Parchman, Weddle said.

Cox’s writings, which were provided by attorneys with the Office of Capital Post-Conviction Counsel, revealed “the alleged location of the body of Felicia Cox; missing since July of 2007,” said the statement, which added, “Cox has been a longtime suspect in her disappearance.”

“The Pontotoc County Sheriff’s Department and the District Attorney’s Office were in contact with Cox … prior to the execution urging the disclosure,” it said.

Cox shared an admission of guilt and details about his sister in-law’s whereabouts on or about Oct. 26, prosecutors said.

Weddle said Tuesday by telephone that he is hopeful that authorities will find the body of Felicia Cox, who was 40 years old when she vanished.

“The case has been open for a long time, 14½ years. We’ve never had the evidence that we needed to prosecute this,” Weddle said. “He’s always been a suspect because he was one of the last people to see her alive. But he never confessed to it. We didn’t have a body.”

Officials are working on the logistics of searching for Felicia Cox’s remains, and her relatives are optimistic that she will be found, Weddle said. He said the body will be looked for in Pontotoc County.

Authorities have contacted experts in archaeology and anthropology at Mississippi State University to help in the search and recovery if Felicia Cox is found, officials said.

David Cox, 50, last month became the first inmate to have been executed in Mississippi in nine years. He had pleaded guilty to killing his estranged wife and sexually assaulting her young daughter as her mother lay dying more than a decade ago.

Cox exhausted his appeals and filed court papers saying he was “worthy of death.” He appeared calm as he received a lethal injection on Nov. 17. A coroner pronounced him dead at 6:12 p.m.

“I want my children to know that I love them very much and that I was a good man at one time,” Cox said just before the injection started. “Don’t ever read anything but the King James Bible.”

Cox was sentenced to death for the fatal shooting in 2010 of Kim Kirk Cox. He pleaded guilty in 2012 to capital murder and multiple other charges, including sexual assault. A jury handed down the death sentence.

Prosecutors said Cox shot his wife and let her bleed to death over several hours while he sexually assaulted his stepdaughter three times in front of her dying mother.

CORRECTION (Dec. 8, 2021, 11:23 a.m. ET): A previous version of this article misstated when a death row inmate revealed the location of his sister-in-law’s body. It was three weeks before his execution, not two.

Erik Ortiz and Associated Press contributed.