Four people were found dead in a suspected triple murder-suicide spanning two homes on Mercer Island and Issaquah, Washington, following welfare checks requested by an attorney on December 30, 2025.
Danielle Cuvillier, 80, and her son Mackenzie P. Williams, 45, were discovered dead with gunshot wounds at approximately 10:45 a.m. at a residence in the 8400 block of Southeast 46th Street on Mercer Island. Officers initially observed a gunshot wound through a window before entering the home.
The welfare check was requested by an attorney representing the homeowner, who reported receiving a concerning email that raised fears for the occupants’ safety. Inside the residence, officers found both individuals deceased, with four firearms recovered within the home and one additional firearm found in a vehicle.
Following the initial discovery, investigators identified concern for another individual who had previously resided at the Mercer Island location. As a precaution, the Mercer Island Police Department requested the Issaquah Police Department conduct a welfare check at a separate residence.
At 11:37 a.m. the same day, officers were dispatched to a home in the 400 block of Southeast Evans Lane in Issaquah, where they found two additional people dead. The victims were identified as Dominick M. Cuvillier, 34, and Harmony Crystal Danner, 44. Both had sustained multiple gunshot wounds.
There were no signs of forced entry at either location, according to police reports.
On January 2, 2026, the King County Medical Examiner’s Office confirmed the causes and manner of death for all four victims. Danielle Cuvillier’s death was ruled a homicide caused by multiple gunshot wounds to the head. Williams’ death was ruled a suicide. Both Dominick Cuvillier and Danner died from multiple gunshot wounds to the head, with their deaths classified as homicides.
“The Medical Examiner ruled the death of Mackenzie P. Williams a suicide and the death of Danielle Cuvillier a homicide,” Mercer Island Police Commander Jeff Magnan said.
The deaths followed more than a year of documented family conflict over caregiving arrangements for Dominick, who had Angelman syndrome.
Court records reveal the family dispute centered on concerns about proper care and guardianship arrangements for Dominick. The conflict escalated significantly in early 2025 when Danielle Cuvillier was arrested for domestic violence on January 16, 2025.
Following the January arrest, a protection order was filed against Williams. As part of the protection order proceedings, Williams surrendered 53 firearms to authorities. The protection order was subsequently reissued multiple times as the family navigated the legal system.
In August 2025, the parties reached a settlement agreement regarding Dominick’s care. Under the terms of the settlement, Danielle Cuvillier was appointed as guardian and conservator for her younger son, granting her legal authority over both his personal and financial affairs. This appointment formalized her role as his primary caregiver.
The protection order against Williams was terminated on December 10, 2025, less than three weeks before the deaths occurred. The termination of the protection order meant Williams was no longer subject to the firearms restrictions that had been imposed earlier in the year.
The investigation into the deaths remains ongoing, with detectives continuing to review evidence. “Detectives continue to review evidence, including forensic analysis of firearms recovered from the scene,” police stated.
All firearms recovered from both locations have been secured and will undergo ballistics testing to determine which weapons were used in the shootings.
The Mercer Island Police Department worked closely with the Washington State Patrol Crime Scene Response Team during the initial investigation. Crime scene teams conducted neighborhood canvassing and collected physical evidence from both residences.
Authorities emphasized there is no indication of an ongoing threat to the community in either Mercer Island or Issaquah. The incidents appear to be contained to the two residences and involve only family members.
The investigation by both the Mercer Island and Issaquah police departments continues, with additional information expected to be released as forensic analysis is completed. The coordination between the two agencies was crucial in responding to what initially appeared to be an isolated incident but quickly expanded to involve a second location.
