A milk-truck driver carrying three guns stormed a one-room Amish schoolhouse Monday, sent the boys and adults outside, barricaded the doors with two-by-fours, and then opened fire on a dozen girls, killing three of them before committing suicide.
At least seven other victims were critically wounded, authorities said.
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.
The gunman, Charles Carl Roberts IV, a 31-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, State Police Commissioner Jeffrey B. Miller said.
Miller said investigators were looking into the possibility the attack may have been related to the death of one of Roberts' own children.
According to an obituary, Roberts and his wife, Marie, lost a daughter shortly after she was born in 1997.