Killed in the New Year's Eve slayings were the boy's parents, Steven and Linda Kologi, as well as his 18-year-old sister, Brittany, and a family friend named Mary Schultz

Authorities in New Jersey have detained a 16-year-old boy who stands accused of the brutal New Year’s Eve slayings of his parents, sister, and a 70-year-old family friend, PEOPLE confirms.

The suspected killer’s name is not being released because of his age, but prosecutors in Monmouth County announced they would be filing formal murder charges against the teen on Monday.

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A press release from authorities alleges the quadruple homicide was committed with a semi-automatic rifle. A motive for the deaths has not been released by investigators.

Image zoom Brittany Kologi

Image zoom Linda and Steven Kologi

Killed in the New Year’s Eve slayings inside a home in Long Branch were the boy’s parents, Steven and Linda Kologi, who were 44 and 42 respectively, as well as his 18-year-old sister, Brittany, and a 70-year-old family friend named Mary Schultz. Schultz lived in the home with the Kologis, according to prosecutors.

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Monmouth County Prosecutor Christopher J. Gramiccioni addressed the media Monday morning, and said the incident occurred around 11:43 p.m. The teen’s brother and grandfather were also inside the home at the time of the attack.

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“We are investigating this and are confident that it’s a domestic incident that’s completely isolated,” Gramiccioni said, adding that it’s a “terribly tragic incident.”

Image zoom Authorities respond to the crime scene Pix11 News

The teen was arrested without incident, prosecutors say. The alleged murder weapon has been recovered, according to investigators.

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