Four people are dead and seven wounded with at least three in critical condition after a gunman seeking revenge for an incident that had occurred 20 years earlier, opened fire on students in a one-room Amish school house in rural Pennsylvania.

Shortly before 11:00am, a 32-year-old man armed with an automatic handgun entered Wolf Rock School, a one-room Amish school house located in Paradise, Bart Township, Lancaster County, about 55 miles west of Philadelphia, Pennsylvania.

The gunman, who had come well prepared, allowed several adults to leave the building, including a pregnant woman, and three adults with young children, then ordered the male students to get out. The boys ran from the schoolhouse and hid in a nearby field, while the adults, including the teacher who managed to escape along with the others, went for help.

The man, who has been identified as Charles Carl Roberts IV, a milk delivery truck driver, bound the young girls feet together with wire ties and flex cuffs. He then retrieved a shotgun, as well as 2x4s and 6x4s from his pickup truck, and proceeded to barricade himself and the children inside of the school.

Police arrived on the scene at approximately 11:00am and proceeded to try to talk the gunman into giving himself up, while calling out to the girls to get down on the floor. Roberts responded, ordering the police to leave within ten seconds or he would start shooting people. Shortly thereafter, at least ten gunshots were heard. Roberts had lined the children up along the blackboard, shot them in the head executioner style, and then turned the gun on himself.

The exact number of victims has not yet been released; however, four people are confirmed dead, including the gunman. The Lancaster County emergency services dispatched dozens of emergency vehicles, including at least nine ambulances, as well as several police vehicles to the scene. It is believed there were at least 13 girls in the school at the time.

Roberts' wife later told police that the last time she had seen her husband was just before she had left the house on an errand, as he was leaving to take their three children to the bus stop. Upon returning home, Mrs. Roberts found several suicide notes that her husband had left for her and their children. At approximately 11:00, Charles called her to say goodbye, and that she wouldn't be seeing him again. Despite her attempts, he refused to tell her where he was.

According to his suicide notes, the shootings were an act of retaliation for something he'd had to endure some 20 years earlier, at the age of 12. Further details have yet to be released. Police believe that Roberts' hatred was directed at young girls in general, and that he had chosen the school because it was located close to his home.