The suspect was taken into custody without incident following the shooting inside the Wall Street home in Long Branch just before 11:45 p.m.
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He will be charged with four counts of murder and one count of unlawful possession of a weapon.
A semi-automatic rifle was recovered at the scene, investigators said. The rifle used in the shooting was legally registered to a resident of the house.
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The victims have been identified as the suspect's parents, 42-year-old Steven Kologi and 44-year-old Linda Kologi; his sister, 18-year-old Brittany Kologi; and a 70-year-old family friend, Mary Schultz.
Monmouth County Prosecutor Chris Gramiccioni described the shooting as an isolated domestic incident. The motive of the shooting was still under investigation.
"It's a terribly tragic incident," Gramiccioni said.
The teen's name has not been disclosed.
The prosecutor said the teen's grandfather and brother were not targeted and left the home unharmed.