A US man mistakenly shot dead his 15-year-old son while investigating what appeared to be an attempted burglary next door, police say.
Jeffrey Giuliano, from New Fairfield in Connecticut, opened fire on a masked teenager outside his sister's house.
Police later told him he had killed his adopted son Tyler. No charges have yet been filed in the case.
"All in all it's a tragedy," said state police spokesman Lt J Paul Vance, quoted by the AP news agency.
According to police, the father was called by his sister, who lives next door, at around 01:00 on Friday (05:00 GMT) when she heard someone outside the house and believed they were attempting to break in.
Mr Giuliano confronted a person wearing a black balaclava and black clothing, and fired his gun when the person lunged at him with "a shiny weapon".
He did not know it was his son until they removed the head covering.
The teenager was discovered by police lying in the driveway with gunshot injuries, his father sitting nearby. Tyler was pronounced dead at the scene.
No charges have been filed, and an autopsy is planned.
Mr Giuliano is a science teacher in the town's school district.
In a statement to parents, schools superintendent Alicia Roy said: "Our district has experienced a tragedy that has affected us deeply".
"Everybody is just shaking their heads over it," New Fairfield First Selectman John Hodge told the Danbury News-Times on Thursday. "We're hoping the police can get to the bottom of it."