Douglas Herlihy has pleaded guilty to manslaughter after investigators say he beat his father to death in Milford in 2003, when he was 17.
The plea was part of a negotiated plea agreement filed Wednesday in Hillsborough County Superior Court in Nashua.
Under the plea deal, Herlihy will serve between 12 and 24 years in prison. Per the agreement, second-degree murder charges will be dismissed.
The attorney general’s office said Herlihy, 40, also pleaded guilty to attempted falsification of physical evidence in the crime. His father, Paul Herlihy, 50, died from blunt force trauma.
Police arrested Herlihy in June 2025 in Saugus, Mass., and he was extradited to New Hampshire to face charges in the cold case murder.
Court documents indicated Herlihy told acquaintances that his father was abusive and that he took steps to evade being detained in Massachusetts and New York, the Union Leader reported.
A sentencing date will be scheduled sometime in early 2027.
The investigation was led by the New Hampshire Cold Case Unit, New Hampshire State Police, and the Milford Police Department.
