From the article:
The wounded man happened to be walking by at the time and was caught in the crossfire.
Officer Chad Perez, who was patrolling the area, led the pursuit of the teenager after Perez saw him running in an alley. He chased the suspect along with back-up officers he had requested, police said. They arrested the boy in the 2200 block of North Johnson Street.
The injured, according to an NOPD news release, are the 12-year-old girl shot multiple times in both legs; a 20-year-old man found in the 2200 block of North Galvez Street with a gunshot wound to his right shoulder; 18-year-old woman shot in her thigh; and 24-year-old woman shot in her hip and jaw.