Prosecutors in New Hampshire will tell a judge Friday that a teenager who admitted to killing his sister-in-law and her two sons in 2022 should spend nearly a century behind bars.

Eric Sweeney, who is now 19, was 16 when he fatally shot Kassandra Sweeney, 25, and her sons, 4-year-old Benjamin and 23-month-old Mason, at their home in Concord.

Sweeney pleaded guilty in August to lesser second-degree murder charges. He was originally charged with murder in the first-degree.

Eric Sweeney, escorted by an officer, enters court on Friday, Aug. 15, 2025 at Merrimack County Superior Court in Concord, N.H. Prosecutors are seeking a sentence of at least 97 years after he pleaded guilty to second-degree murder in the 2022 deaths of his sister-in-law and two nephews. (Geoff Forester/ Concord Monitor via AP, Pool, File)

“We are asking the court to grant Eric some measure of mercy,” attorneys Lauren Prusiner and Morgan Taggart-Hampton wrote in a sentencing memorandum made public Thursday.

They said he loved those he killed and will “grapple with the consequences of his actions for the rest of his days.”

Eric had been living with his brother Sean and Kassandra for about three years, and they were acting as his guardians. 

Tensions had grown between the brothers, who were barely speaking, and Sean grew so worried he installed a lock on the door to his master bedroom, according to court documents. 

Sean and his wife wanted Eric out of their home and had begun taking steps to have him removed, according to the filing.

On Aug. 3, Eric allegedly snapped. He removed one of Sean’s two guns, a .40 Taurus handgun, from a locked safe, then allegedly gunned down his nephews and sister-in-law in the kitchen of the three-bedroom home. 

Kassandra was struck once in her right eyebrow, and both boys were shot in the crown of their heads.

Eric Sweeney, then 16, gunned down his nephews Benjamin and Mason Sweeney, pictured, and their mom, Aug. 3, 2022, in New Hampshire. (Facebook)

Without providing a motive for the killings, his defense lawyers wrote that “his depression deepened. He knew he was on the brink of losing the safest, most loving home he had ever known.”

Minutes before the killings, Kassandra had fixed snacks for her children and was filming them playing and laughing to send to her husband. Kassandra was a nursing assistant who worked nights so she could care for her boys during the day.

Sean, who drove an oil delivery truck at the time, was on his route when Eric called from Kassandra’s iPhone and claimed “someone broke in and killed them all.”

Shortly after police arrived, Sean pulled up, followed by Eric behind the wheel of Kassandra’s silver Ford F-150.

The Northfield, New Hampshire, home where Eric Sweeney allegedly shot his nephews and sister-in-law to death Aug. 3, 2022.  (Google maps)

In an interview with investigators, Eric said he was in the basement when he heard something break, then a “deep, male voice yelling followed by multiple ‘pops.'”

He told police he crept upstairs and “stepped over Kassandra and Mason’s bodies” to exit the house, the motion says.

Although tree workers were at the end of the driveway, he didn’t ask them to call for help.

He allegedly tossed the weapon from the driver’s side window on I-93 before returning to the house, according to the Merrimack Superior Court filing.

Fox News’ Rebecca Rosenberg and The Associated Press contributed to this report.