Prison guard hit by stray bullet from nearby shooting range

A prison guard at the state prison in Otay Mesa, California was struck in the back of the head by a stray bullet as he was standing inside the prison grounds, near the perimeter fence. The bullet grazed his head and knocked him to the ground. At first he thought someone had hit him with a rock but an investigation determined that a bullet had come from the nearby firing range where a local law enforcement agency was training. The outdoor range is located about 300 yards from the main prison compound.
The guard was treated at the local hospital for a graze wound and sent home to recuperate.
Initially, investigators thought the bullet was a ricochet from the firing range, but they are also exploring the possibility that it was a misfire from a semi-automatic handgun, with the bullet taking an upward trajectory and then falling into the prison compound.
Ohh shoot.