A New Hampshire teenager who once alleged that home invaders murdered his sister-in-law and young nephews, ages 4 and 1, is now preparing to admit guilt in their deaths, according to a court document.

Eric Sweeney, 19, plans to confess to the murder of Kassandra Sweeney, 25, along with her sons, Benjamin and Mason, who was only a month short of his second birthday. He intends to plead guilty to three counts of second-degree murder and one count of tampering with physical evidence, as outlined in the court filing. Sweeney is scheduled to formally enter his plea during a court hearing on Friday, per the report from local ABC station WMUR.

The Merrimack County grand jury indicted Eric Sweeney on three first-degree murder charges for the killings, which happened just after his 16th birthday, state Attorney General John M. Formella announced in October 2023. The charge of falsifying evidence relates to his disposal of the Taurus .40 caliber handgun used in the murders, as stated by Formella.

Court documents detailed tensions within the household shared by Eric Sweeney, his brother Sean Sweeney, and the victims in the weeks before the slayings on August 3, 2022, at their home in Northfield, approximately 20 miles from Concord. The older sibling was the defendant’s legal guardian, and they resided together in the same house.

Prosecutors noted that the defendant failed to adhere to “house rules,” including taking food and using tools without permission, while also allegedly crafting makeshift weapons. These actions led to arguments with his brother and sister-in-law, causing a “deteriorating” relationship, according to the state.

Just under two weeks before the murders, Sean Sweeney expressed fear for his family’s safety upon discovering weapons in his garage and the surrounding woods, the New Hampshire Union Leader reported, 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.”