It was a horrific scene in a Long Branch, New Jersey home on New Year’s eve after a 16-year-old boy fatally shot his parents, sister and a family friend just before midnight.

Monmouth County Prosecutor Christopher J. Gramiccioni said that the boy — whose name was not released — was taken into custody without incident. The teen’s brother and grandfather, who were home at the time of the shooting, managed to escape unharmed, authorities said Monday.

“We are confident that this is a domestic incident that is completely isolated,” Gramiccioni said, noting that Long Branch police responded to the home at about 11:43 p.m. Sunday. “It’s a terribly tragic incident.”

Gramiccioni did identify the deceased: Steven Kologi, 44; Linda Kologi, 42; Brittany Kologi, 18; and Mary Schultz, 70. Schultz was identified as a “family acquaintance” by the prosecutor’s office.

Gramiccioni said that the teenager used a semi-automatic assault rifle, which was legally owned and registered to a family member, in the murders.

He declined to comment on the suspect’s motive or a possible mental disability when asked by reporters. He said the attack was an “isolated” domestic incident.

The teenager is expected to be charged as an adult, Gramiccioni said.