A 20-year veteran sheriff's deputy in Central California was killed by a bullet in the chest from a colleague's gun in what officials said Tuesday appeared to be "a tragic accidental shooting."

Deputy Sgt. Rod Lucas was having a conversation with a detective about how to carry their backup weapons when the shot was fired on Monday, Fresno County Sheriff Margaret Mims said. The incident occurred at a sheriff's office near the Fresno Yosemite International Airport.

Mims said Lucas, 46, and the detective were in a room with two other colleagues and there was no dispute, just a conversation about weapons safety.

"The detective had his weapon out. During this discussion, the detective's weapon discharged," the sheriff said. "Sgt. Lucas was struck by the bullet in his chest, and he dropped to the ground."

Lucas was immediately given CPR and rushed to Community Regional Medical Center, where he died.

Mims did not disclose the type of firearm involved in the incident, calling it "an improved secondary weapon for the detective." She said all witnesses have been interviewed except for the detective, who was not identified, due to his mental state which she described as extremely upset.

"We do not know yet the mechanics of how the weapon discharged," Mims said. "So far, we have absolutely no reason to believe this was anything more than a tragic accidental shooting."

During an emotional news conference, Mims described Lucas as a father of four and a well-liked, respected officer who joined the Fresno County Sheriff's Office in 1996.

"He truly was a leader, in the best terms I can describe," Mims said. "We are hurting right now. We're hurting."

Lucas' death marked the 12th officer to die in the line of duty in Fresno since the sheriff's office opened in 1856, Mims said.