Devyn Black pleaded guilty in D.C. Superior Court to aggravated assault while armed and possession of a firearm during a violent crime.
Black had started a summer internship in Councilman Jim Graham's office four days before the June 18 shooting, and Graham went with Black when the teenager turned himself in to police.
Black was riding the Metro at about 3 p.m. when he saw a person he had a fight with about a month before, officials said. According to prosecutors, Black and his friends followed the person up the escalator, where Black shot him in both legs. One of the bullets also struck a bystander in the leg.