[ sires ] all of it enough to bring flooding oh motions from parents and terrified teens. calling and calming and calling my son. like, come here. for us, too, that isn t fair. reporter: police say 18-year-old timothy simpkins is in custody. just after a fistfight discharged his gun around 9:00 in the morning injuring four people. one critically. he s facing three counts of aggravated assault with a deadly weapon. we need help! reporter: arlington pd confirms they re investigating this video showing one student picking up another and slamming him slefrl times, but not confirming identity of anyone in the clip. [ gunfire ] nor are police discussing what appears to be six shots heard in this video on the second floor down the hallway, a tenth grader hid behind a desk. i was shocked. numb. couldn t believe this was happening. reporter: 12 hours later her