NICKEL MINES, Pa. - A fourth child died Tuesday of wounds from the shootings at an Amish schoolhouse in Lancaster County.

The 7-year-old girl died about 4:30 a.m. at Penn State Children's Hospital in Hershey, hospital spokeswoman Amy Buehler Stranges said.

"Her parents were with her," Buehler Stranges said. "She was taken off life support and she passed away shortly after."

The girl was wounded Monday in the attack, the nation's third school shooting in less than a week, in a bucolic area of Lancaster County.

Charles Carl Roberts IV, apparently spurred by a grudge two decades old, wrote his wife what authorities described as suicide notes, took guns and ammunition and went to a nearby one-room schoolhouse, where he killed the girls, critically injured six more, and took his own life, authorities said.

A 6-year-old girl remained in critical condition and a 13-year-old girl was in serious condition at Penn State Childrens, Buehler Stranges said. She said the names of the children were not being released.

Three girls, ages 8, 10 and 12, were flown to Children's Hospital of Philadelphia, where they were out of surgery but remained in critical condition, spokeswoman Peggy Flynn said.

One other victim was taken by helicopter to Christiana Hospital in Delaware, where officials declined to release information.

Roberts, a 32-year-old from nearby Bart Township who was not Amish, did not appear to be targeting the Amish and apparently chose the school because he was bent on killing young girls as a way of "acting out in revenge for something that happened 20 years ago," said state police Commissioner Jeffrey B. Miller.

"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," Miller said.

The names of the dead were not immediately released.

The attack bore similarities to a deadly school shooting last week in Bailey, Colo., but Miller said he believed the Pennsylvania attack was not a copycat crime. "I really believe this was about this individual and what was going on inside his head," he said.

According to investigators, Roberts dropped his children off at their bus stop, then at about 10 a.m. pulled up at the school, which had about 25 to 30 students ranging in age from six to 13.

Roberts brought with him supplies necessary for a lengthy siege, including three guns, a stun gun, two knives, a pile of wood and a bag with 600 rounds of ammunition, police said. He also had a change of clothing, toilet paper, bolts and hardware and rolls of clear tape.

He released about 15 boys, a pregnant woman and three women with infants, barred the doors with desks and wood and secured them with nails, bolts and flexible plastic ties. He then made the girls line up along a blackboard and tied their feet together.

The teacher and another adult fled to a nearby farmhouse, and authorities were called at about 10:30 a.m. Miller said Roberts apparently called his wife from a cell phone at around 11 a.m., saying he was taking revenge for an old grudge. Miller declined to say what the grudge could have been.

"It seems as though he wanted to attack young, female victims," Miller said.

Moments later, Roberts told a dispatcher he would open fire on the children if police didn't back away from the building. Within seconds, troopers heard gunfire, and found his body when they were able to get inside.

From the suicide notes and telephone calls, it was clear Roberts was "angry at life, he was angry at God," and co-workers said his mood had darkened in recent days, Miller said.

In a statement released to reporters, the gunman's wife, Marie Roberts, called her husband "loving, supportive and thoughtful."

"He was an exceptional father," she said. "He took the kids to soccer practice and games, played ball in the backyard and took our 7-year-old daughter shopping. He never said no when I asked him to change a diaper."

"Our hearts are broken, our lives are shattered, and we grieve for the innocence and lives that were lost today," she said. "Above all, please pray for the families who lost children and please pray too for our family and children."

In the attack last week at Platte Canyon High School in Bailey, Colo., a man singled out several girls as hostages in a school classroom and then killed one of them and himself. Authorities said the man in Colorado sexually molested the girls.

On Friday, a school principal was shot to death in Cazenovia, Wis. A 15-year-old student, described as upset over a reprimand, was charged with murder.

Neighbors who knew the Roberts' family said they saw no indications of trouble brewing.

"They're a fine Christian family. It's ironic and it's heartbreaking," said Lois Fiester, a relative of Roberts who was standing outside the family's modest tan ranch house.