A milk-truck driver carrying three guns and a childhood grudge stormed a one-room Amish schoolhouse, sent the boys and adults outside, barricaded the doors with wood planks, and then opened fire on a dozen girls, killing three people before committing suicide.
At least seven other victims were critically wounded, authorities said.
It was America's third deadly school shooting in less than a week, and it sent shock waves through Lancaster County's bucolic Amish country, a picturesque landscape of horse-drawn buggies, green pastures and neat-as-a-pin farms, where violent crime is virtually nonexistent.
Most of the victims had been shot execution-style at point-blank range after being lined up along the chalkboard, their feet bound with wire and plastic ties, authorities said. Two young students were killed, along with a female teacher's aide who was slightly older than the students, state police Commissioner Jeffrey B. Miller said, reports AP.
"This is a horrendous, horrific incident for the Amish community. They're solid citizens in the community. They're good people. They don't deserve ... no one deserves this," State Police Commissioner Jeffrey B. Miller said.
Miller told Fox News late Monday that a fourth girl had died at Hershey Medical Center. However, a spokeswoman for the hospital, Amy Buehler Stranges, said that there had been no change in the condition of the three girls at that hospital.
State police spokeswoman Trooper Linette Quinn said Miller's information had come from crime scene investigators, and she could not explain the discrepancy.
The gunman, Charles Carl Roberts IV, a 32-year-old truck driver from the nearby town of Bart, was bent on killing young girls as a way of "acting out in revenge for something that happened 20 years ago" when he was a boy, Miller said.