Greg Sikes was the estranged brother of Marine Captain Todd Newell. The two were both born and raised in Smokey Corners but at a young age, their parents separated.
Todd's mother took him with her while Greg was left behind with his father who refused to let her have both of their children taken away.
Several years later, Greg rang Todd, informing that their mother had died and then called him again, seeking help as he was under attack from Ritt Everett and a group of people who were active in a feud that had been active in the town for ten years.
Unfortunately, Greg was presumbly shot during the fight and the cabin he was in was set on fire with his badly burned body later being discovered by a group led by Curtis Teague who were searching for Greg's brother, Todd who had gone missing.
Greg's remains were brought back to NCIS where the Medical Examiner Donald Mallard told Leroy Jethro Gibbs that despite the fact there was a bullet wound, Ducky stated that he would never be certain about the cause of death.
Abigail Sciuto later discovered a connection that the entire team had missed: Greg and Todd were actually brothers.
Everitt and Sheriff Miller Thompson were both eventually arrested for Greg's death while it was later discovered that Ritt's daughter, Daphne was carrying Greg's baby.