A 16-year-old New Jersey boy armed with a semi-automatic rifle shot and killed his parents, sister and a family friend inside the family home less than 30 minutes before midnight on New Year’s Eve, authorities said on Monday.

Local prosecutor Chris Gramiccioni said the boy would be charged with four counts of murder and a weapons offence stemming from the shooting in the shore town of Long Branch.

Police have not speculated on a motive for the shooting. The rifle used in the shooting was legally registered to a resident of the house, Gramiccioni said.

The boy’s name was not disclosed but the victims were identified as his parents, Steven Kologi, 44, and Linda Kologi, 42; his 18-year-old sister, Brittany; and 70-year-old Mary Schultz, who lived with the family.

Police responded to a 911 call reporting shots fired at the home just after 11:30pm on Sunday, Gramiccioni said. He described the shooting as an isolated domestic incident and said the teenager was taken into custody without issue.

The boy’s grandfather and brother were not targeted and left the home unharmed.

“It’s a terribly tragic incident,” Gramiccioni said, adding that charges were expected to be filed late on Monday.

The boy was expected to make an initial court appearance on Tuesday, and prosecutors were considering whether to seek to move the case to an adult court.

Jalen Walls, 18, a neighbour who went to school with Brittany Kologi, told NJ.com that he frequently went to the Kologis’ house. He said the 16-year-old boy required special assistance and was cared for by his mother. The teenager did not attend the same public schools as his siblings, Walls said.

“But he was fully functional and comprehended what we were saying,” Walls added.

Another family friend recalled seeing Steven Kologi recently.

“I could never have believed this could have happened. They were all good people,” Carmen Gaudious told the Asbury Park Press, a New Jersey daily newspaper.

“I just spoke to Steve three days ago. He looked good. It was cold so we didn’t say much. He wished me happy holidays.”