CONCORD — A 19-year-old man, formerly of Northfield and accused of slaying his sister-in-law and two young nephews in 2022, pleaded guilty to three second-degree murder charges and one charge of falsifying evidence in front of a visibly tense courtroom on Friday.

The motive remains unknown as to why Eric Sweeney, who was 16 at the time of the murders, acted the way he did.

Earlier this week, on Aug. 13, Sweeney filed a naked plea in Merrimack County Superior Court for the murder of Kassandra Sweeney, 25, and her two children, Benjamin Sweeney, 4, and Mason Sweeney, 23 months, shot on Aug. 3, 2022, in their Northfield home.

A naked plea is a guilty plea with no negotiations with the prosecution. The Honorable Judge John C. Kissinger Jr. presented questions to Sweeney, confirming his ackn

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