Court documents said Robert Wayne Gladden, a student at Perry Hall High School, "shot at one of the first tables in the cafeteria and struck Daniel Bowory in the back" shortly before 11 a.m. Monday, the first day of the school semester.
Witnesses said they described hearing a sound like a bag of chips popping before anyone realized a shooting was in progress, The Baltimore Sun reported Tuesday.
Police at a Tuesday news conference said Gladden was charged as an adult with attempted first-degree murder and assault. He brought a dismantled shotgun, 21 shells and a bottle of vodka to school, they said, adding they did not believe he was impaired at the time of the shooting, and that police are aware Gladden was a bullying victim but do not think it connected to the shooting.
Borowy, 17, remains in critical condition at Maryland Shock Trauma Center in Baltimore, a hospital spokeswoman said.
Court documents said police seized a range of items, from schoolwork to weapons, from the house Gladden shares with his mother and stepfather, the newspaper reported.
Police said they have also charged the stepfather, Andrew Piper, 43, alleging he owned weapons illegally due to prior convictions.