On December 30, 2025, following welfare checks in two separate residences in Mercer Island and Issaquah, Washington, four individuals, including an elderly woman and her two sons, were found dead. The authorities have declared the incident a triple murder-suicide linked to a dispute over the care of a disabled family member.
80-year-old Danielle Cuvillier and her 45-year-old son, Mackenzie P. Williams, were found dead from gunshot wounds during a welfare check at their Mercer Island residence. Williams’ death has been ruled as suicide, while Cuvillier’s murder has been classified as homicide. They both suffered from multiple gunshot injuries.
The welfare check was initiated by an attorney at about 10:45 a.m. on a Tuesday. Upon arrival, the officers discovered the bodies of the victims.
After the horrifying discovery on Mercer Island, a second welfare check was conducted at an Issaquah residence. Here, two more victims were found: 34-year-old Dominick Cuvillier, Danielle’s younger son, and 44-year-old Harmony Danner, Williams’ wife. Both Danner, a physical therapist, and Dominick, who had Angelman syndrome, died from multiple gunshot wounds, and their deaths were declared homicides.
Investigators found no evidence of forced entry in either of the residences. They recovered four firearms from the Mercer Island home and a fifth from a car. Williams was known to have owned over 50 firearms and had surrendered 53 during legal proceedings earlier that year.
Police later said they believe Williams shot the three other family members before taking his own life. Investigators said there was no evidence that anyone else was involved and that the killings appeared to be confined to the family. Authorities reiterated that there was no ongoing threat to the public.
The deaths occurred after a year-long legal battle between Cuvillier and Williams regarding the guardianship and care of Dominick.
The family feud escalated on January 16, 2025, when a confrontation at Cuvillier’s residence led to her arrest on suspicion of domestic violence. Following this incident, Cuvillier submitted a vulnerable adult protection order against Williams on January 28, 2025.
On November 10, 2025, the court appointed Danielle as Dominick’s guardian, granting her the authority to manage his personal and financial matters. The protection order was revoked on December 10, 2025, less than three weeks before the tragic incident took place.
The Mercer Island Police confirmed that the victims had visible gunshot wounds and stated that there was no threat to the wider public.
The King County Medical Examiner’s Office has concluded its preliminary examinations and released the causes and manners of death for all victims. The forensic analysis of the firearms from both locations, however, will require additional time, according to investigators.