He was killed when officers opened fire on an aggressive pit bull and a bullet ricocheted and struck him in the chest.
The deputies had first been called to the Palmdale complex at about 3:45 a.m. with complaints of a loud party.
The dog, which belonged to the boy's neighbor, had already bitten one of the deputies and the teen had restrained it behind the apartment complex when it broke loose and charged again, Los Angeles County sheriff's officials said.
The boy was struck in the chest as he tried to pull the dog away.
The boy was taken to a hospital with gunshot wounds, where he was pronounced dead.
Los Angeles Sheriff Captain Christopher Bergner called the boy's death "an extremely, extremely unfortunate incident".
Garcia-Muno was the oldest of four siblings. When the deputies made a decision to try and corral the dog to prevent anyone else from being attacked, they noticed Armando on the ground, wounded.
Bergner said both the teen and the deputy may have been hit by a " skip" round that ricocheted off the ground.
Amber Alcantar, Garcia's aunt, told the Los Angeles Times that her nephew was shot while trying to stop the pit bull from attacking deputies a second time.
The family identified the teen as Armando Garcia-Muro, according to the Los Angeles Times. "Our initial impression was (the deputies) didn't even see the individual coming around from the side of the building".
The dog was eventually captured by the deputies and taken to animal control, who plan to euthanize the pit bull.
The dog, she said, is a 3-year-old blue-nosed pit bull that was usually well-mannered when off its leash.
The woman also told the newspaper her apartment was used as a hangout for local teenagers who "come over and listen to music".
She claimed that her dog is well mannered and off his leash, which was a normal practice, and feels that the deputies' claims about the dog seem questionable. He was about to enter his senior year of high school.
She said her nephew lost his life trying to save a friend's dog. "He was a very loving person", the boy's mother told the LA Times, adding that he loved dogs.
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