MARTINSVILLE, IN --Dustin Tatum was leaving his middle school cafeteria Friday when he heard a loud bang, then chaos ensued as a teacher rushed him and several fellow students into a classroom, locked the door, turned off the lights and ordered everyone to hit the floor. Only later did Tatum learn his close friend, a 15-year-old classmate, was shot in the stomach and that police were identifying the alleged shooter as a former student expelled from the central Indiana school just days earlier. "It was a nightmare hearing my friend just got shot and he's being lifelined to the hospital," said Tatum, 14. The lone victim, Chance Jackson, was listed in critical but stable condition Friday evening at Methodist Hospital in Indianapolis, where he was taken by helicopter. The former 15-year-old student suspected in the attack was arrested miles away on the south side of Martinsville about an hour after the shooting, which unfolded before 7 a.m. Friday, just as classes were about to begin, State Police Sgt. Curt Durnil said. The teen was being questioned at the county jail as Morgan County prosecutors reviewed possible charges against him. "We have no motive at all at this point. We're talking to witnesses and schools officials to get to the bottom of it," Durnil said. Officers found a handgun believed used in the shooting in a field near the school about 30 miles south of Indianapolis. The shooting just inside a school entrance on the last day of classes before the start of spring break sparked an hours-long lockdown at Martinsville West Middle School, as hundreds of panicked parents awaited word on their children. The school, with about 600 students and 39 teachers, is one of two middle schools in the city. Durnil said the teen in custody had been suspended then expelled from the school this week and was not supposed to be on campus. He said he did not know why the student was expelled, and school officials would not comment. But Tatum and other classmates told The Associated Press that Jackson and the shooting suspect had a volatile relationship and had argued. Morgan Lanfair, an 18-year-old student at a local high school, said she was friends with Jackson and the suspect and that they'd had a conflict recently but that neither discussed it with her. She said the suspect had been in trouble at school but that she didn't think he "would go through with something like this." Jackson's family released a statement Friday afternoon asking the public to pray "for the families of all involved." Tonya Haltom, a 36-year-old Martinsville resident, said her son is a classmate and close friend of the shooting suspect. She said she was "dumbfounded" when a friend knocked on her door Friday morning and told her the news. She said the suspect "is actually a very good kid. I mean he had some issues, but (he) usually talked to me. But this time he didn't talk to me." Tobi Berkholz, whose son grew up with the suspect, said she never heard the suspect argue. "He would do anything he could. It's like he just wanted to fit in. He just wanted to be liked," she said. Many parents who gathered to pick up their children Friday were angry that they had heard about the shooting on the news or through calls or text messages from their children and questioned why the school didn't send an alert until more than an hour after the shooting. "It was ridiculous," said Sandy Pitman, who has a son in seventh grade at the school. Assistant Superintendent Randy Taylor said during an afternoon news conference that the school district had a plan in place and carried it out. He did not take questions. "We all hope a situation like today will never happen, but unfortunately, today it did," he said.