WARREN, N.J. (CBSNewYork/AP) —  A northern New Jersey man fatally shot his fiancee and her brother Sunday before turning the gun on himself, authorities said.

John Reno, 48, killed Heidi Errickson, 45, after they argued Sunday afternoon at their Warren Township home, Somerset County prosecutors said Monday. He then killed Frederick Errickson Jr., 55, who was shot in the driveway shortly after he arrived at the home, apparently to check on his sister’s welfare.

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The shootings sparked a standoff with law enforcement officers that lasted for about six hours.

Reno eventually was found lying in a drainage ditch in a dense wooded area in the rear of the home. He had a self-inflicted fatal gunshot wound to the head, authorities said.

An assault rifle with two high-capacity magazines was found next to Reno’s body, authorities said.

Some nearby homes were evacuated as a precaution, but residents were allowed to return Sunday night. Many said the shooting was out of character for the normally quiet, affluent town, WCBS 880’s Kelly Waldron reported.

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Police investigate a double murder-suicide in Warren, New Jersey, on Aug. 17, 2015. (Credit: Kelly Waldron/WCBS 880)

Police investigate a double murder-suicide in Warren, New Jersey, on Aug. 17, 2015. (Credit: Kelly Waldron/WCBS 880)

“I was shocked,” said Kevin, who has worked in the town for years. “Like Warren? Wow! It could happen anywhere.”

“It was just something that you never think about it,” one woman said. “I mean, our neighbors don’t even lock their doors.”

“Horrible to think that someone can do something like that, and I’m just very sorry for the friends and family of people who were the victims,” said Cora, who lives in nearby Watchung.

Cora also said she’s a firm believer in stiffer gun-control laws, and Sunday’s shooting only confirms that belief.

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