Four people, including an 80-year-old woman and her two adult sons, were found dead in separate homes on Mercer Island and in Issaquah, Washington, following welfare checks on December 30, 2025. Authorities have ruled the deaths as a triple murder-suicide stemming from a family dispute over the care of a disabled adult.
Danielle Cuvillier, 80, and her son Mackenzie P. Williams, 45, were discovered dead with gunshot wounds during a welfare check at a home in the 8400 block of Southeast 46th Street on Mercer Island. Williams’ death was ruled a suicide, while his mother’s death was classified as a homicide. Both suffered multiple gunshot wounds.
The welfare check was requested by an attorney around 10:45 a.m. Tuesday morning. When officers arrived at the residence, they found both victims deceased.
Following the discovery on Mercer Island, investigators requested a second welfare check at a home in the 400 block of Southeast Evans Lane in Issaquah. There, officers found two more victims: Dominick Cuvillier, 34, and Harmony Danner, 44. Dominick, who went by Nick, was Danielle’s younger son and Williams’ brother. Danner was Williams’ wife and worked as a physical therapist. Both died from multiple gunshot wounds, and their deaths were ruled homicides.
Investigators found no signs of forced entry at either location. Four firearms were recovered inside the Mercer Island home, and a fifth firearm was found in a car. Williams owned more than 50 firearms and had surrendered 53 firearms during legal proceedings earlier in the year.
The deaths followed more than a year of legal conflict between Cuvillier and Williams over the care and guardianship of Dominick, who had Angelman syndrome.
The family dispute escalated dramatically on January 16, 2025, when a confrontation ensued at Cuvillier’s home, and Cuvillier was arrested on suspicion of domestic violence.
Following the January incident, Cuvillier filed a vulnerable adult protection order against Williams on January 28, 2025.
The court appointed Danielle as Dominick’s guardian on November 10, 2025, granting her authority over his personal and financial affairs. The protection order was terminated on December 10, 2025, less than three weeks before the four family members were found dead.
Mercer Island Police confirmed that officers found the bodies with obvious gunshot wounds and stated there was no threat to the public at large.
Neighbors in both communities expressed shock at the violence.
The Mercer Island Police Department continues to investigate the circumstances surrounding the deaths, with assistance from the Washington State Patrol Crime Scene Response Team. Detectives are reviewing evidence and conducting forensic analysis of the firearms recovered from both scenes.
Authorities have stated that there is no ongoing threat to the public and no outstanding suspects. The investigation remains active as detectives continue to piece together the exact sequence of events that led to the four deaths.
The King County Medical Examiner’s Office has completed its initial examinations and released the causes and manners of death for all four victims. The forensic analysis of the firearms recovered from both locations will take additional time to complete, according to investigators.
