Angus Kelly, 78, was wounded in a shootout with the men June 28.
Moore County Sheriff Lane Carter told ABC11 in June that four men robbed the Short Stop convenient store on U.S. Highway 1 in the Lakeview area.
Clerk Grace Kelly - who is in her 70s - was closing the store for the night and husband was in the parking lot waiting for her.
When Angus saw what was happening, Carter said he came to his wife's aid with a shotgun and fired through the store's glass doors with a shotgun - hitting one alleged robber in the face. A gunfight ensued, and both Kellys were wounded.
Grace Kelly was treated and released from Moore Regional Hospital for a gunshot wound to the arm.
Angus Kelly was shot in the torso. He was rushed to UNC hospitals in Chapel Hill for surgery, but he never recovered.
Four men were arrested in the case. Paris Yusef Mack, 17, of Richards Street in Southern Pines, Randy Joel Williams, 17, of Shaw Avenue in Southern Pines, Demarcus Dennison, 18, of Polkton in Anson County and Leroy Medley, 20, of Southern Pines all face robbery and assault charges.
Prosecutors were expected to add more charges following the death of Angus Kelly. The Moore County Sheriff's Office said in a news release Friday that detectives were scheduled to testify before a grand jury on Monday as prosecutors seek murder indictments.