Two days after David Neal Cox lay strapped to a gurney and was put to death by lethal injections last month, his lawyers hand-delivered a letter to the district attorney’s office in Tupelo, Miss., that could solve a 14-year-old cold case.

Cox, 50, confessed to the 2007 slaying of his sister-in-law, Felicia Cox, and detailed where he buried her body, District Attorney John Weddle announced Monday at a news conference.

“We would like to stress that locating the remains of Felicia Cox is not a foregone conclusion,” said Weddle, whose jurisdiction includes several northern Mississippi counties. “We are hopeful that the information is accurate and that recovery efforts will be successful so that Felicia’s family may give her a proper burial.”

Cox’s Nov. 17 execution broke a nine-year death penalty hiatus in Mississippi. Cox pleaded guilty in 2012 to murdering his estranged wife, Kim Kirk Cox, and to several other charges, including sexually assaulting his stepdaughter. Cox later waived all appeals, calling himself “worthy of death” in a letter to the Mississippi Supreme Court.

“I seek to be executed,” he wrote in 2018. “Please grant me this plea.”

Cox had a history of violence, his stepdaughter, Lindsey Kirk, told the Associated Press. She witnessed Cox use methamphetamines and said he sexually assaulted her “for a few years.” When she told her mother in 2009 about the abuse, she called police. Cox was arrested and faced several charges, including statutory rape, child abuse and sexual battery.

He was released from jail on bond in April 2010 to await trial. Kirk Cox, then 40, filed a restraining order against her estranged husband and moved herself and her three children into her sister’s home.

One month after Cox’s release, he fired a gunshot through the screen door of Kirk Cox’s sister’s house and stormed in, according to court documents. He then shot Kirk Cox in the arm and abdomen and sexually assaulted 12-year-old Lindsey three times as her dying mother was forced to watch. A standoff with police lasted over eight hours before Cox was finally arrested.

Law enforcement long suspected Cox was also responsible for the 2007 disappearance of his brother’s wife, Felicia Cox. Kirk Cox was the last person to see Felicia, then 40, before she went missing, according to police.

In the weeks leading up to Cox’s execution, the Pontotoc County Sheriff’s Department and the district attorney’s office urged him to confess, Weddle said.

In late October, Cox admitted his guilt to his lawyers with the Office of Capital Post-Conviction Counsel and provided the alleged location of his sister-in-law’s body, according to the district attorney. Cox also waived attorney-client privilege effective after his death. The lawyers delivered the confession on Nov. 19.

Weddle said police expect to search for Felicia Cox’s body “in the coming days.” Authorities would not provide any details about the location but noted they will be using equipment that will allow them to detect a body underground.

“We have contacted experts in archaeology and anthropology with Mississippi State University to assist the search and recovery if located,” Weddle added.