A 16-year-old New Jersey boy gunned down his parents, sister and a family friend just before midnight on New Year's Eve, turning the family home into a bloodbath that his brother and grandfather managed to escape, investigators said Monday.

The teenager shot and killed his father, mother, sister and a family friend who also lived in the Long Branch, N.J., home, Monmouth County Prosecutor Christopher J. Gramiccioni said in a statement. Police were called to the home around 11:43 p.m., and the suspect was taken into custody without incident, Gramiccioni said.

“We are confident that this is a domestic incident that is completely isolated,” Gramiccioni said. “It’s a terribly tragic incident.”

The boy’s name was not released because he is a juvenile, but the Monmouth County Prosecutor’s Office identified the deceased as: Steven Kologi, 44; Linda Kologi, 42; Brittany Kologi, 18; and Mary Schultz, 70. Schultz was identified as a “family acquaintance” by the prosecutor’s office.

The suspect’s brother and grandfather also were at the home at the time of the shooting but were able to escape unharmed, Gramiccioni said during a Monday news conference.

The teenager was believed to have used a Century Arms "semi-automatic assault rifle" to gun down his family members and the family friend, authorities said during a news conference. The gun was legally owned and registered to a family member, Gramiccioni said.

Gramiccioni declined to comment on the suspect’s motive or a possible mental disability when asked by reporters. He did say the attack was an “isolated” domestic incident. Police also said there was no known history of violence at the house.

"The Kologis were very caring, loving people and always looking to do fun things with their kids," Walter Montelione, Linda Kologi's cousin, told WCBS-TV. "He was a good kid. He was a little, you know, slow with learning disabilities, but he knows right from wrong."

Brittany Kologi was a freshman at Stockton University in Galloway Township, N.J., where she studied health sciences, a university spokeswoman confirmed to Fox News.

"We are shocked and saddened by the reports of the death of freshman Brittany Kologi under such tragic circumstances," Diane D'Amico, a Stockton University spokeswoman said. She added that counseling staff will be on hand for students.

Veronica Mass, 69, told NJ.com that her daughter and Linda Kologi were friends who grew up together. She said she was “stunned” by the shooting.

“They were a close-knit family,” Mass told the publication. “No drugs, no alcohol.”

She also said that the suspected shooter had been home-schooled. He had a hard time keeping up with his peers academically and was picked on by other students, she said.

But, Mass said the suspect “improved dramatically after being home-schooled” and was “outgoing, very friendly. He would tell jokes.”

An older brother of the suspected shooter reportedly posted a touching tribute to his slain family on Instagram, calling his parents “the greatest parents I could ask for.” Steven Kologi Jr. said his parents made sure to provide for their children – with food, a home and at Christmastime – even though “they struggled financially.”

“I cannot even describe the type of people they were so just believe me when I say how great they were,” he said.

As for his sister, the surviving Kologi called her “so beautiful and smart.”

“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 because I didn’t do it enough,” he said.

Jalen Walls went to school with Brittany Kologi and lives a few blocks away from the home. He also told NJ.com that the suspected shooter was cared for by his mother as he required special assistance.

"But he was fully functional and comprehended what we were saying," Walls said.

In a Facebook tribute, Dave Farmer said he played softball with Steven Kologi and “never had an argument or disagreement since” with him.

‘I’m proud to say publicly that I knew and loved this man unconditionally and always told him when we parted, ‘I love you brotha!!!’” Farmer said.

The teenager could be charged as an adult, officials said.

Monmouth County Prosecutor’s Office and the Long Branch Police Department have launched a joint investigation into the murders.

A GoFundMe account has been set up to help with the funeral expenses and has raised nearly $20,000 as of Tuesday morning.