Police were called to a home in the city of Long Branch, about 55 miles (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.
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.
Get Breaking news, live coverage, and Latest News from India and around the world on NDTV.com. Catch all the Live TV action on NDTV 24x7 and NDTV India. Like us on Facebook or follow us on Twitter and Instagram for latest news and live news updates.