From an article:
The teenager, whose name is not being released, shot a juvenile during a house party in the 3500 block of Mars Court the evening of Oct. 13, according to the Tracy Police Department. The victim's injury was not life-threatening. Police arrested the suspect about 2:15 p.m. on Thursday.
Detectives were able to piece together the teen's involvement in the case through witness statements and collected evidence, police said.
The article doesn't say how the boy was able to access a loaded gun.
Every gun in the hands of a child must first pass through the hands of an adult.