The man who stormed a one-room school and killed five girls apparently chose the schoolhouse because it was an easy target rather than because he had a grudge against the Amish, police said.
Pennsylvania police said the dairy truck driver (32) said the man lost a child of his own three years ago, and they were investigating suicide notes that he left as well as statements he made to his wife that he was seeking revenge for something that occurred 20 years ago.
Two girls died overnight, bringing to five the number of students killed, police said today.
The two girls who died overnight were aged seven and eight, said Commissioner Jeffrey Miller of the Pennsylvania state police. One other girl remained in critical condition, and another four were described as stable.
Commenting on Roberts' motive, Mr Miller said the death of a child three years ago may have affected his state of mind.
"He may have been angry with God for having lost a child," Mr Miller said at a news briefing.
The third deadly US school shooting in a week shattered the calm of an Amish farm community where there is little crime.
"We don't believe that he had . . . some animus toward the Amish community. We believe that this was a target of opportunity," Mr Miller said. "He believed he could get in there pretty easily and secure it from a defensive posture."
The gunman, identified as Charles Carl Roberts, 32, was not Amish and had no prior criminal record.
Several members of the Amish community interviewed said they were sad and disappointed but not angry and emphasised the need for forgiveness.
"It's just not the way we think. There is no sense in getting angry," said Henry Fisher (62), a retired farmer who has lived all his life in the town some 60 miles west of Philadelphia.
He also said he did not expect additional security such as locks on schools because this was a "freak accident".
According to the Lancaster Eranewspaper, Roberts and his wife, Marie Roberts, had a daughter who died as an infant.
They also have two sons and a daughter, ranging in age from 18 months to seven, the paper said.
Mr Roberts walked his older children to a school bus stop in the morning, waited until his wife left the house, left suicide notes for his family and then drove a borrowed pickup truck to the Amish school.
He dismissed the boys in the school, as well as the teacher and some other adults. Surrounded by police around 45 minutes after he entered the school, he made brief calls by cellphone to his wife and to police and then opened fire on his victims.
Roberts fired three rounds from a shotgun and 13 from a pistol, police said, shooting the children "execution style" in the back of the head.