Suffolk County police investigate the scene near a home, at...

Suffolk County police investigate the scene near a home, at right, on Selden Road in Mastic Beach after an early morning 911 call reporting a stabbing. (June 10, 2013) Credit: James Carbone

A 13-year-old boy stabbed his mother's ex-boyfriend to death with a kitchen knife early Monday after the man barged into their Mastic Beach home armed with a gun and confronted the woman and her new boyfriend, Suffolk County police said.

"It appears he [the youth] was defending his mother from a violent and potentially fatal attack," Det. Lt. Jack Fitzpatrick of the Homicide Squad said. He said no charges were filed.

The incident occurred, police said, when Norman Shields, 48, who most recently lived in Brooklyn, entered the Mastic Beach home about 3:45 a.m. and got into "a domestic dispute" with his former girlfriend, Natasha Bivens, 31. Their 4-year-old daughter also was in the house and was not harmed.

Once inside, Shields "produced a gun and started to assault the woman," a police spokesman said. Fitzpatrick said Shields was trying to force his way into the bedroom and Bivens was trying to hold him off.

Shields fired one shot from the revolver he was carrying, but no one was struck by the bullet, Fitzpatrick said.

At that point, the son, whose name was not made public, stabbed Shields several times on the left side of his body with a kitchen knife, Fitzpatrick said.

Bivens' current boyfriend fled the house at some point, Fitzpatrick said.

Shields was taken to Brookhaven Memorial Hospital Medical Center in East Patchogue, where he was pronounced dead, police said.

Neighbor Ellie Dammeyer said she didn't hear arguments or shouting coming from the house around the time of the stabbing. The family, she said, has lived there for about three or four years and were "a quiet people."

About two summers ago, she said, the boy and his friends helped her clear her yard.

"It's a shame," Dammeyer said. "I feel bad for him."

Shields, 48, had an extensive criminal record dating to 1981, when he was arrested on a drug charge at age 16, records show.

He gave Bivens' rental house on Selden Road as his home address when he was arrested last year and sentenced to time served on a misdemeanor charge of possession of marijuana. He served three separate terms in state prison over the years on charges of drug possession, assault and robbery, records show.

Telephone messages left Monday at Bivens' house were not returned.

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