The boy made a 911 call about 9:45 a.m. to report the shooting in the 8800 block of Jefferson Street in La Mesa. Officers and medics arrived to find the 17-year-old girl suffering from a bullet wound to the upper left side of her body, Lt. Matt Nicholass said.An ambulance crew took the victim, who was conscious and alert, to Sharp Memorial Hospital in San Diego for treatment of the apparently non-life threatening injury.The girl's wound was reported to be through and through, and she was expected to be released from the hospital later Monday evening. Her brother told investigators he had inadvertently fired the AR-15 while handling it in a dining area next to the room where the girl was watching television."He was accidentally playing with a gun and the gun discharged and shot somebody inside the house," said Nicholass. "He was scared, very shocked.""This is a weapon that can cause serious injury. Had this been three or four inches either direction we could be looking at a dead child," Nicholass added. The round went through the victim's shoulder and into the sofa, according to Nicholass.Police say no adults were home at the time. It was not immediately clear if the boy or his parents might face any type of criminal charge, such as negligent use of a firearm, or if the weapon was properly registered, Nicholass said."These types of weapons need to be locked up in a house; they need to be secured," said Nicholass. Neighbor Todd Messenger was shocked at the event, and he told 10News, "This is outrageous. I can't believe they'd leave a gun lying around where a kid could get to it. It just seems absurd to me."