As CBS News Correspondent Jane Clayson reports, police don't know what caused a seemingly good kid to turn bad.
People who knew the alleged assailant, James R. Sheets, described a quiet eighth-grader, a member of the school football team, an avid skateboarder and basketball player.
"We don't know why today. And we don't know why, period," Red Lion Borough Police Chief Walt Hughes said after the shootings Thursday. "I think it's safe to say that something was building inside of him that he couldn't control."
An estimated 350 students were gathered in the cafeteria Thursday morning before classes when the shootings occurred at Red Lion Area Junior High School, about 30 miles southeast of Harrisburg in south-central Pennsylvania.
Principal Eugene Segro, 51, shot once in the chest with a 44-caliber Magnum, was pronounced dead on arrival at York Hospital, York County Coroner Barry Bloss said.
Sheets died at the scene of a single shot to the head from what police believe was a .22-caliber weapon, he said. Police said Sheets also had brought a .357 caliber Magnum. Police believe he acted alone.
"All of a sudden, he just stands up and shoots the principal ... and then I saw him shoot himself in the head," said Angel Williams, 14, who knew Sheets and was sitting at a nearby cafeteria table with her sister and friends.
The guns Sheets allegedly used in the shootings belonged to his stepfather, police said. Sheets had used a key to remove them from a safe at his house, police said.
Officials did not know of any school or legal problems the boy was facing, and said his mother, Angelia Baker, and stepfather, Arthur Baker, had not seen any warning signs.
Police later searched the Baker home, seeking computer files, notebooks, weapons and other items, according to a search warrant. They removed a computer and numerous bags and boxes, officials said.
A message left at the Baker home Thursday was not returned.
"They're upset, distraught," Hughes said.
Sheets was an athletic teen who played on the school football team and could often be found skateboarding or shooting hoops in his rural subdivision, neighbors and fellow students said.
Danica Shirey, 14, whose locker is next to the one Sheets used, described him as a boy who never got into trouble and who was friendly with everyone, although he rarely spoke unless spoken to first.
"He never had a problem with anybody," said the eighth-grader.
Segro, who lived in York, had been the school's principal for the past seven years, and served as vice principal for eight years before that, school officials said.
"Gene was an outstanding person, an outstanding principal," Red Lion Area School District Superintendent Dr. Larry Macaluso told CBS' Early Show. "He was truly an instructional leader of his school. He handled the school in a very positive, soft, but firm and consistent manner. He had a great deal of integrity and had the trust of his staff, students, and the parent community as well."
"He tried to find the most lenient way to punish the kids. It wasn't just a job for him. He truly loved the kids," said Nicole Wisor, 16, a 10th-grader who had attended the school.
Segro's wife, Lynne, is a teacher at Jacob Devers Elementary School in York. The couple has one child, a daughter who attends an in-state college, said York schools spokeswoman Debi Beshore.
The junior high school's approximately 875 students were dismissed for the day and students at two nearby schools also were sent home. The junior high was to remain closed Friday.
Counselors were being made available to students, and several hundred parents and students attended an informational meeting at the senior high school on Thursday night.
The junior high school does not have metal detectors but does have security cameras, according to Terry Robinson, the school district's business manager.