From the article and news video:
Los Angeles police were unable to confirm to The Times on Friday morning that someone was in custody, but Officer Rosario Herrera said: "We know it was an accidental discharge, but we don't know if it was a self-inflicted wound or if there's a suspect involved."
The shooting victim was rushed to the hospital after the incident Thursday in the 10000 block of Telfair Avenue. He was in listed in critical condition, Herrera said.
She said it was not clear whether the boy lived in the Pacoima home where the shooting occurred or if he was connected to the tenants.
KTLA-TV reported that one person was detained and two others fled on foot after the incident. The station also said the gun had not been located. City News Service also reported that a boy had been detained.UPDATE (5/2/12): On April 20, a boy was taken into custody, but no further information was revealed.