Three teenagers who broke into a home in Oklahoma were killed by the homeowner's son firing an assault-style AR-15, say police.
"They were dressed in black, all had masks on, and all had gloves on," Deputy Nick Mahoney told reporters.
The intruders - who police say were armed with brass knuckles and a knife - were shot by a 23-year-old man in an act of "self-defence", officers said.
The son may not face charges due to so-called stand your ground laws.
"This may be a case of 'stand-your-ground,' however, it's still too early to say for sure, and we're still looking into all aspects of this," Mr Mahoney told local media.
He was referring to the laws in some states that say a citizen can legally use lethal force if they feel that their life in is imminent danger.
Two of the teenagers died inside the home and one ran outside before dying in the driveway.
The teenagers broke through a sliding glass door in the back of the house before encountering the homeowner's adult son, who was armed with an AR-15 assault-style rifle, police say.
The man, who authorities say also lives at the address with his father, opened fire on the teens after they had a "short exchange of words".
Authorities say they have no reason to believe the home residents knew the teens.
Two of the teens are under 17 years old and one is between 18 and 19.
A fourth person has been arrested and is facing murder and burglary charges.
Elizabeth Marie Rodriguez, 21, turned herself in at the Broken Arrow police station and has admitted to serving as a getaway driver.
Nearby residents tell local media that there have been a string of burglaries in the area, but police have made no link.