A gunman who killed five girls in an attack on a Pennsylvania Amish school told his wife he had molested two young members of his family 20 years ago.
Charles Carl Roberts, 32, made the claim in a phone call to his wife just before he started shooting the girls.
He also made references to an incident 20 years ago in suicide notes and said he had been haunted by dreams of repeating his actions.
Police said it was possible his attack on the girls was sexually motivated.
Five girls remain in hospital - one is critical and one is in serious condition. Three are described as stable.
"He said 'I am not coming home', and he states 'I molested some minor family members that were three and four years old 20 years ago,'" Pennsylvania police commissioner Jeffrey Miller said of Roberts' call to his wife.
Mr Miller said there was no evidence that any of the girls at the school had been sexually abused.
However, he said Roberts had been equipped with a "restraint kit" and two tubes of lubricant gel, which he could have been planning to use in a sexual assault.
Mr Miller pointed out that all of the victims were young girls aged six to 13 and that all of the older women and males in the classroom had been made to leave.
Mr Miller said that all members of Roberts' family, including two who were aged between three and five years old 20 years ago, had been interviewed following his abuse confession, but all said they had no knowledge of any such molestation occurring.
Roberts would have been aged 11 or 12 at the time of the claimed abuse.
His wife Marie and other family members have said he was a good and loving husband and father and that prior to Monday's attack there had been no hint of what he was planning.
In both the suicide notes and the call to his wife, Roberts spoke of his trauma following the death of his infant daughter Elise nine years before.
Elise was born premature in 1997 and only survived for 20 minutes.
Roberts said that following the girl's death his life had "changed forever" and that he was angry at God and himself.
Although not Amish himself, Roberts was a milk lorry driver who delivered to the community.
Police say Roberts had meticulously prepared for the attack, purchasing a stun gun and tools some days in advance and compiling a checklist of gear.
Investigations are under way to establish when and where Roberts got the pistol, rifle, shotgun and 600 rounds of ammunition that he had with him.
"He had a mental script that he had already gone through in his mind and plans for what he was going to do until the time that the police arrived," Mr Miller said.
Change of plan
However, police believe that when state troopers arrived at the school and surrounded it, it disrupted Roberts' plan and caused him to panic.
The hostage crisis quickly descended into a bloodbath as Roberts began shooting the girls, whom he had tied and lined up in front of the blackboard. He then turned the gun on himself.
By the time police stormed the building, three girls and the gunman were dead.
Two more girls - a nine-year-old and a seven-year-old - died in hospital.
Two of the girls killed were sisters. Another family lost one daughter and had one injured.
The injured girls are a six-year-old, two eight-year-olds, an 11-year-old and a 13-year-old.
The six-year-old remains critical and the 13-year-old is described as being in a serious condition.
FACTS ABOUT THE AMISH
Anabaptist Christian denomination
Communities in the US and Canada
Many communities reject links to outside world
Most Amish shun modern technology including electricity and cars
Plain clothing - no buttons allowed in some communities
Speak English and a German dialect called Pennsylvania Dutch
US President George W Bush said that he and his wife Laura were "saddened and deeply concerned" by the shootings and two others which occurred in US schools in the past week.
"We grieve with the parents and we share the concerns of those who worry about safety in schools," Mr Bush said.
Last Wednesday a 16-year-old girl died when an armed man, who also killed himself, took six students hostage at a Colorado high school.
And on Friday, a Wisconsin high school principal was killed when he confronted an armed 15-year-old student as he entered the school.
The White House has said it plans to host a conference on gun-related violence in schools on Tuesday following the bloodshed.