SALT LAKE CITY — Police are investigating what caused a security guard working at the Salt Lake City Main Library to accidentally fire his gun Sunday, sending a bullet through two walls.

Police responded when a CBI security guard reported he had accidentally discharged his firearm about 30 minutes before the library opened Sunday, Salt Lake City Police Lt. Josh Scharman said. 

"No one was injured," Scharman said. "There were minimal employees and no patrons in the library at the time."

Reports indicate the bullet travelled through two walls before becoming lodged in a third, Scharman said. Police are investigating what the man was doing at the time the weapon went off as he prepared for his shift, and will also inspect the gun to determine whether it malfunctioned, he said. 

Contributing: Paul Nelson