A 17-year-old has been charged as an adult in the murder of his sister-in-law and his two nephews in their Northfield home one year ago, authorities announced Wednesday.

Eric Sweeney was indicted by a Merrimack County Grand Jury on three counts of first-degree murder for purposely causing the deaths of Kassandra, 25, Benjamin, 4, and Mason Sweeney, 1, by shooting them, according to New Hampshire Attorney General John Formella.

Each died of a single gunshot wound, authorities said.

Kassandra grew up in Northwood and graduated from Coe Brown Academy. Her family said Kassandra was born to be a wife and a mother.

“She spent every available moment making family memories whether it was with her husband and sons, at her parents’ house, with her sister, or with extended family,” her obituary said. “Kass spent many hours playing in the yard with her boys, sharing meals, decorating and celebrating holidays (especially Christmas with her family), and spreading love.”

Benjamin loved singing “Puff the Magic Dragon” and cooking with his mother, according to his obituary.

“He was a lover of learning whether it numbers, letters, animals or nature,” his obituary said. “Benjamin enjoyed making memories with his family and extended family.”

Mason, who was about to turn two years old, was just building his first memories.

“Mason loved cuddling with his family, dancing to The Beach Boys ‘Barbara Ann’ and ‘Baby Shark,’ ” his obituary said.

Kassandra’s husband, Sean Sweeney, was cooperative with investigators and devastated by the loss of his family, authorities said.

Police officers who responded to a 911 call found the three bodies inside the Northfield home on Aug. 3, 2022.

Sweeney was also indicted on one count of falsifying physical evidence, accusing him of trying to alter, destroy, conceal, or remove a Taurus .40 caliber handgun, with the purpose of thwarting a criminal investigation.

Sweeney is currently being detained and will be arraigned at a future date.

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