An 16-year-old boy was taken into custody after his parents, sister and a family friend were killed on New Year’s Eve. Police found the bodies of Steven Kologi, 44, Linda Kologi, 42, Brittany Kologi, 18, and Mary Schultz, 70, inside their Long Branch, New Jersey home that day.

The unidentified boy was taken into custody without incident, according to CNN.

“Thankfully, it was uneventful,” Monmouth County Prosecutor Christopher Gramiccioni said of the arrest. “It didn’t require any force.

A press release about the killings said it appeared a “Century Arms semiautomatic rifle” was used. The gun was legal and registered to an unidentified family member, according to Gramiccioni. The boy did not have a criminal history, according to CBS News.

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

The boy was reportedly autistic, according to the New Jersey Patch. Veronica Mass, a friend of Linda Kologi, told the boy had “emotional problems.” Mass also described the family as “close knit” and said the boy was “outgoing” and “very friendly.”

“He improved dramatically after being home schooled,” Mass said. “He learned to read, did his math. He got up to where he was supposed to be.”

Another sibling, Steven Jr., and the boy’s grandfather were both inside the home at the time but managed to escape.

“I just wish I could tell all of them how much they meant to me and how much I truly loved each and every one of them,” Steven Jr. wrote in an Instagram post, according to the New York Daily News. “Because I didn’t do that enough.”

The motive for the killings remained unclear. The boy, who was being held at Middlesex Youth Detention Facility, was expected to appear in court Tuesday to be charged. Prosecutors said they intended to try him as an adult.

“The Kologis were very carrying, loving people and always looking to do fun things with their kids,” Walter Montelione, Linda Kologi’s cousin, told CBS News. “He was a good kid. He was a little, you know, slow with the learning disabilities, but he knows right from wrong.”