An 80-year-old artist, along with her two sons and daughter-in-law, was discovered dead early Tuesday morning in what appears to be a triple murder-suicide in a wealthy suburb of Seattle.
Local police reported that Daniel Couvillier, 80, and his son, Mackenzie P. Williams, 45, were found deceased in their Mercer Island home, located just 11 miles from downtown Seattle.
A few hours later, authorities found two more bodies—a woman in her 40s and a man in his mid-30s—in a home in Issaquah, which is about 27 miles outside of Seattle. This discovery came during a welfare check by police.
Mercer Island Police Chief Jeff Magnan later communicated that he informed Issaquah authorities about the deaths of Daniel and Williams and requested checks on Daniel’s 34-year-old son, Dominique Couvillier, and Williams’ wife.
Daniel’s attorney indicated that Dominique was one of the victims found at the Issaquah residence, while neighbors confirmed that Williams’ wife was the unidentified second victim.
The police are investigating Daniel and Williams’ deaths as murder-suicides, although they have not yet identified who might have been responsible.
Daniel was noted to have a passion for art and photography, sharing her works on Instagram over several years.
According to reports from Mercer Island Police, four firearms were retrieved from the Mercer Island home, with a fifth found in a vehicle at the scene.
The incident in Issaquah is being viewed as a homicide. It was reported that both individuals discovered there had been shot, and there were no signs of forced entry.
Inconsistencies within the family were prevalent, as court documents revealed ongoing conflict between Daniel and Williams concerning the care of Daniel’s second son, who has Angelman syndrome, a rare genetic condition requiring extensive, round-the-clock support.
Dominique had lived with his parents until 2018 when his father passed away. After that, Williams took on the responsibility of managing his care alongside his mother.
Williams accused Daniel of abusing Dominique, both physically and mentally, which Daniel denied, according to various media sources.
In January 2025, Ms. Williams began proceedings to secure power of attorney with her brother’s agreement, granting her full control over Dominique’s care.
Daniel contested this, alleging that William had manipulated his brother into giving up control.
A family dispute escalated to legal actions, including an assault charge against Daniel’s mother for an altercation with Williams. Daniel sought a protection order against Williams for the sake of Dominique, citing Williams’ erratic behavior and the concerning number of firearms in his possession.
Documents revealed that Williams had admitted to owning 53 firearms, which he later surrendered.
The protective order against Williams was approved and renewed multiple times but was ultimately lifted in early December.
In August, Daniel and Williams reached an agreement allowing Dominique to live with his mother, with visitation rights granted on specific days to minimize conflicts.
The investigation into the deaths remains open, with the King County Medical Examiner’s Office tasked with determining the cause and manner of death for all involved.
