Police were called to a home in the city of Long Branch, about 90 kilometers south of New York, at 11:43 pm Sunday in response to a report of shots fired and found four people dead, Monmouth County Prosecutor Christopher Gramiccioni said in a statement.
The victims were the suspect's father Steven Kologi, 44; mother Linda Kologi, 42; sister Brittany Kologi, 18; and family friend Mary Schultz, 70.
The suspect's brother and grandfather were apparently unharmed. They "thankfully left the home and came out OK," Gramiccioni said at a press conference Monday, according to ABC News.
Prosecutors did not release a motive for the killings, which the boy carried out with a Century Arms semiautomatic rifle, prosecutors said.
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The teenager, whose name was not released, was taken into custody without incident.
He was expected to be charged as an adult with four counts of murder and one count of possession of a weapon for an unlawful purpose.
