"I will approach the high court seeking life imprisonment for the juvenile accused," he said.
The JJB, presided over by principal magistrate Geetanjali Goel, sentenced the lone minor accused to a three-year stay in a special home.
The boy, who was 17-and-half years old at the time of the incident, has turned 18.
Four other accused are facing separate trial in a fast track court. One accused died during trial.