LONG BRANCH — A 16-year-old boy is in custody after he shot and killed three relatives and a friend living in the home with a semi-automatic rifle on New Year's Eve, according to the Monmouth County Prosecutor's Office.

The teen opened fire inside a home at 635 Wall Street around 11:45 p.m. Sunday night, killing his father, Steven Kologi, 44, his mother, Linda Kologi, 43, an 18-year-old sister, Brittany, and 70-year-old family friend Mary Schultz, Prosecutor Christopher J. Gramiccioni said.

A brother and grandfather were also at the home but escaped unharmed, according to Gramiccioni. Police were alerted to the shooting by a 911 call from within the home.

The prosecutor said the incident was the first time police had been to the address. If investigators knew what motivated the teen, they were not saying publicly Monday morning.

The suspect was quickly taken into custody by Long Branch and the Monmouth County Sheriff's Department, according to Gramiccioni, who would not disclose the identity of the gunman because he is underage and had not yet been charged. He said the arrest was "uneventful."

Gramiccioni, however, said they will seek to try the teen as an adult on four counts of first-degree murder and a charge of second-degree possession of a firearm for an unlawful purpose.

The gun, described as a Century Arms semi-automatic rifle, was legally registered to a member of the family, according to Gramiccioni.

The teen is expected to appear before a Superior Court judge Tuesday morning.

EDITOR'S NOTE: This story was updated to include more information about the weapon prosecutors say was used.

Contact reporter Dan Alexander at Dan.Alexander@townsquaremedia.com or via Twitter @DanAlexanderNJ