Man learns intruder he killed is his son 28 (UPI) -- A teacher in Connecticut killed an intruder at his sister's home and then learned the intruder was his 15-year-old adopted son, police said. Jeffrey Giuliano, who teaches fifth grade and science at Meeting House Hill School, went to his sister's home -- next door to his -- around 1 a.m. Thursday after she called to tell him she heard someone break in. When he got there he encountered the intruder, dressed in black and wearing a ski mask. Giuliano -- who was armed with a handgun -- said he fired when the intruder lunged at him. When the ski mask was lifted, he learned he had killed his stepson, Tyler Giuliano, The (Danbury, Conn.) News-Times reported Friday. Connecticut State Police said Tyler Giuliano -- a 10th-grader at New Fairfield High School who turned 15 Aug. 2 -- had a weapon but they didn't describe it. A neighbor, Lydia Gibbs, said she heard nine gunshots. "I thought it was fireworks because nobody would think it was a shooting in this town," she said. Police said no motive had yet been determined for Tyler Giuliano's actions, the newspaper reported. An autopsy was to be performed Friday.