The Pinellas County Sheriff's Office said Moises Zambrana, 48, was showing his Ruger 9mm pistol to Dustin Bueller, 20, about 12:30 p.m. in the recreation room at Grace Connection Church in Lealman, near St. Petersburg, when the weapon discharged, firing a bullet through a wall and into the head of Hannah Kelley of St. Petersburg, Bueller's girlfriend and the daughter of the congregation's pastor, Tim Kelley, the Tampa Bay Tribune reported.
"It does appear this was a tragic accident," sheriff's spokeswoman Cecilia Barreda said.
Hannah Kelley was listed in critical condition Sunday night after surgery, the sheriff's office said.
Zambrana, of Pinellas Park, has a concealed weapons permit and records indicate he is a licensed security officer, the newspaper said.
No charges had been filed.