Pittsburgh police have charged a 16-year-old student with shooting three others outside a high school, allegedly in retaliation for a drug-related robbery inside the school last month.

None of the students wounded minutes after Brashear High School dismissed classes Wednesday has life-threatening injuries. Police say two were grazed by bullets, while one was shot in the arm and foot. Police say a fourth was targeted but not hurt.

The school, with about 1,400 students, will be open the rest of the week on a modified lockdown, restricting the building to students, teachers and visitors with prearranged appointments.

Police Lt. Kevin Kraus says the alleged shooter, Anjohnito Willett, shot the others as revenge for the Oct. 18 incident. He was in custody Wednesday. It wasn't known if he has an attorney.