Katie Song After 18 years of leading “NCIS,” Mark Harmon has stepped away from his high-profile camera role on the popular CBS criminal drama.Monday’s episode of “NCIS,” the fourth episode of Season 19, concluded with his character Leroy Jethro Gibbs, who was nearly killed in a boat explosion in the Season 18 finale, deciding not to return to his job in NCIS. “I’m not going back, Tim,” said Gibbs to Special Agent Timothy McGee (Sean Murray).