A New Hampshire teen who initially claimed home invaders murdered his sister-in-law and nephews, ages 4 and 1, is planning to plead guilty in their deaths, a court filing shows.

Eric Sweeney, 19, intends to admit to killing Kassandra Sweeney, 25, and her sons Benjamin and Mason, who was just a month shy of his second birthday. Sweeney plans on entering a guilty plea to three counts of second-degree murder and one count of falsifying physical evidence, the filing says. Sweeney will formally enter the plea at a court hearing on Friday, local ABC affiliate WMUR reports.

A grand jury in Merrimack County indicted Eric Sweeney for three counts of first-degree murder in the slayings, which occurred just after his 16th birthday, state Attorney General John M. Formella announced in October 2023. The falsifying evidence charge stemmed from his destroying or getting rid of the Taurus .40 caliber handgun used in the slayings, Formella said.

Court filings described a tense household between Eric Sweeney and his brother Sean Sweeney and the victims in the weeks leading up to the Aug. 3, 2022, slayings at the home in Northfield, some 20 miles north of Concord. The older brother was the defendant”s guardian, and they all lived together in the home.

According to prosecutors, the defendant was not following “house rules,” which included taking food and using tools without permission. He was also allegedly building makeshift weapons. This would spark arguments between him and his brother and sister-in-law, which resulted in a “deteriorating” relationship, the state concluded.

Just 12 days before the killings, Sean Sweeney said he feared for his family’s safety after he found weapons in his garage and surrounding woods, reported the New Hampshire Union Leader, citing police logs.

He called the police in early June and late July 2022 about problems he was experiencing with someone close to the family. The first call was about the car being taken, while the other was about the weapons. The name of the subject of the calls was redacted. No arrests were made, but the person told a police officer that he would change his behavior, the logs said, according to the Union Leader.

On the day of the killings, Sean Sweeney left for work early in the morning, leaving his wife, kids and brother alone. Kassandra Sweeney took videos of her kids playing. They were wearing the same clothes in which they were found dead, prosecutors noted. The defendant claimed he was upstairs and heard “pops” coming from downstairs. He went to investigate and found the victims’ bodies. Before calling 911, the defendant called his brother on Kassandra Sweeney’s phone to inform him what had happened, prosecutors noted.

He told cops it was a home invasion murder and he had nothing to do with it. After he was placed in the back of a police cruiser, he was recorded saying “not my nephews” and “I swear to God, if they don’t catch this f—ing person,” prosecutors said.

But family members were quick to point the finger at Eric Sweeney. His father told detectives, “Eric must have done this,” prosecutors wrote.

Investigators also found gunshot residue on the defendant’s hands.

As Law&Crime previously reported, the AG’s office and law enforcement announced the arrest of Eric Sweeney eight days after the murders; however, they did not release his name due to his age.

Senior Assistant Attorney General Geoffrey Ward told reporters in the days after the shooting that Sean Sweeney had been cooperative.

“He is obviously beyond devastated as a result of these crimes,” Ward said.

A GoFundMe page set up by family member Alizabeth Dawson for memorial costs and living expenses raised over $50,000.

On the day of the homicides, her family “received some of the worst and most devastating news imaginable.” Dawson described her cousin Kassandra Sweeney as “one of the most genuine and beautiful people you could ever meet” and her sons as “two beautiful baby boys.”