Police in Washington State are investigating a suspected murder-suicide after four members of the same family were found dead in two homes near Seattle.
Authorities said an 80-year-old mother and one of her sons were discovered dead inside a home on Mercer Island. Hours later, another son and a daughter-in-law were found dead at a separate residence in Issaquah.
Highlights
- Four family members were found dead in two Seattle-area homes in a suspected murder-suicide involving an 80-year-old mother and her sons.
- Mercer Island officers discovered mother Danielle Cuvillier and son Mackenzie Williams with gunshot wounds after a welfare check prompted by a concerning email.
- Issaquah police found the youngest son and a daughter-in-law dead in a second home, all victims confirmed as related family members.
- The family had ongoing conflict over care of the youngest son with Angelman syndrome, involving legal battles and accusations of abuse and power struggles.
The Mercer Island Police Department (MIPD) said officers responded to a welfare check at about 10:45 a.m. on Tuesday, December 30. The home was located on the 8400 block of Southeast 46th Street.
Four family members were found dead between two houses near Seattle in a suspected murder-suicide
Image credits: Google Maps
According to a news release shared on Facebook, “The request originated from an attorney representing the homeowner, who reported receiving a concerning email that raised fears for the occupants’ safety,” the release noted.
“Upon arrival, officers looked through a window and observed an individual inside the residence who appeared to have suffered a gunshot wound.
"Officers made entry into the home and located two deceased individuals ... Firearms were found within the residence and in proximity to the individuals,” the statement added.
Image credits: Mercer Island Police Department/Facebook
Police later identified the deceased as Danielle Cuvillier, 80, and her son, Mackenzie P. Williams, 45. Based on early findings, police said the case appears to involve a homicide followed by a suicide. The Daily Mail reported that it was Williams who committed the murders.
“There is no indication of an ongoing threat to the community,” the MIPD said.
Out of concern for another family member who previously lived at the Mercer Island address, investigators asked the Issaquah Police Department to conduct a welfare check at a second property.
Issaquah police said officers responded to a home on the 400 block of Southeast Evans Lane. Inside the house, they found two more people dead. Authorities confirmed the bodies of a “female in her mid-40’s and a male in his mid-30’s” were found.
Image credits: Danielle Cuvillier/Instagram
Police later confirmed that all four victims were related. According to reports from The Seattle Times, the man found in Issaquah was Cuvillier’s youngest son, while the woman was married to one of the brothers.
Lawyers of the family told news outlet Kiro that the name of the younger brother was Nick Williams.
They said in a statement, “Danielle’s friends and family are in a state of shock, grief and utter disbelief at the news of her and her loving son Nick’s deaths. We need time and space to mourn appropriately and will release a full statement when we have had time to process this devastating sequence of events.”
Image credits: King 5 Seattle/YouTube
In a follow-up update on December 31, Mercer Island police said investigators recovered four firearms from the Mercer Island home. Officers also found another firearm inside a vehicle connected to the case.
“Investigators continue to work closely with the King County Medical Examiner’s Office to determine the official cause and manner of death,” police said.
Court records and media reports indicate the deaths followed more than a year of conflict within the family over the care of the youngest son, who had been diagnosed with Angelman syndrome. The condition causes severe developmental delays and requires 24-hour care.
According to a King County court declaration cited by The Seattle Times, Williams had reportedly accused his mother of being physically and emotionally abusive to his disabled brother.
The family had been having a conflict over the care of the youngest son, who had Angelman syndrome
Image credits: King 5 Seattle/YouTube
Cuvillier denied these allegations and was granted guardianship of her younger son in November after filing a petition, Fox 13 Seattle reported.
She was a well-regarded artist who sold her work to a local wine bar on the ritzy island, one of the richest zip codes in the U.S.
Cuvillier then accused Williams of encouraging his younger brother to give him power of attorney. In January 2025, Williams had also met with a lawyer and begun working toward assuming power of attorney, with his brother’s consent.
But Cuvillier accused her younger son of being “unduly influenced” to relinquish control to Williams, The Seattle Times reported.
The outlet also noted that Williams had attempted to visit his brother at the Mercer Island home in the weeks leading up to the suspected murder-suicide, but Cuvillier had not let him in.
Image credits: Mercer Police Department
After Williams called 911, Cuvillier was charged with fourth-degree assault in the Mercer Island Municipal Court.
Cuvillier then filed a petition for a protection order against Williams on behalf of her younger son, citing Williams’ “behavior [had] been unpredictable and aggressive lately,” per the outlet.
She was also allegedly concerned about the number of firearms Williams had in his home.
Nico Morales, a local taco vendor, said that Nick Williams ate at his truck daily.
He told the Daily Mail that the younger son was mentally handicapped and could not speak. Still, he would brighten the vendor's day with “signs and hugs.”
“All I know is that every day he would come and eat with us at our food truck,” Morales said.
He described Cuvillier as an “easygoing lady,” who was “sweet and kind.”