A US teacher shot dead a masked teenager he feared was trying to break into his sister's home - only to discover it was his 15-year-old son.
Jeffrey Giuliano, 44, received a phone call from his sister, who lives next door, saying she believed a burglar was attempting to break into her property in the quiet Connecticut town of New Fairfield.
The fifth-grade school teacher grabbed a handgun and went outside to confront the prowler, who was dressed all in black and wearing a ski mask.
He opened fire when the suspect lunged at him with "something shiny" in his hand, according to police.
When officers arrived at the scene, Mr Giuliano was sitting on the grass next to his sister's home and the teenager was lying in the driveway with gunshot wounds and a knife in his hand.
He was pronounced dead at the scene.
It was only when police removed the intruder's ski mask that Mr Giuliano was told he had fatally shot his 15-year-old son Tyler.
No charges have been brought against Mr Giuliano over the boy's death, which police are describing as "tragic".
State police spokesman Lieutenant J Paul Vance said the teenager had never been in trouble with the law, and some of those who knew him described him as a "good kid with an easygoing personality".
He said investigators were at a loss to explain what he was doing outside and carrying a weapon.
It was also unclear if the teen was trying to burgle the house or if it was some type of prank gone wrong.
"Certainly, that is the major question we are trying to answer at this point," Lt Vance said.
"All in all it's a tragedy."
Tyler was adopted by Mr Giuliano and his wife a few years ago, according to friends of the family.
Mr Giuliano was said to be a popular local teacher who was affectionately known as 'Mr G'.
Rosemary Rasile, the mother of one of Mr Giuliano's former pupils, said: "He was the teacher you requested in the fifth grade. He was a great teacher. All the kids loved him."