According to court records and police, a long-running family court dispute involving allegations of abuse, neglect and firearms restrictions preceded a murder-suicide on Mercer Island and two additional deaths in Issaquah that remain under investigation.
All four were identified by the King County Medical Examiner’s Office on Friday.
Police were first called Tuesday morning to a home in the 8400 block of Southeast 46th Street on Mercer Island after an attorney representing the homeowner reported receiving a concerning email that raised fears for the occupants’ safety.
Officers arrived around 10:45 a.m., saw a body through a window and entered the home.
Inside, investigators found two people dead from gunshot wounds.
Police later identified them as Danielle Cuvillier, 80, and her son, Mackenzie Paul Williams, 45.
The King County Medical Examiner ruled Danielle Cuvillier’s death a homicide caused by multiple gunshot wounds to the head and Williams’ death a suicide caused by a gunshot wound to the head.
Police said there were no signs of forced entry at the Mercer Island home.
Investigators located four firearms inside the house and an additional firearm inside a vehicle.
While investigating the Mercer Island deaths, detectives identified concern for another individual who had previously lived at the home.
As a precaution, Mercer Island police contacted Issaquah police to conduct a welfare check at a residence on Southeast Evans Lane.
Issaquah officers arrived at that home around 11:37 a.m. and found two people dead inside.
The King County Medical Examiner identified them as Harmony Crystal Danner, 44, and Dominick M. Cuvillier, 34.
Both deaths were ruled homicides caused by multiple gunshot wounds.
Friends described Danner as a loving physical therapist, who went out of her way to take care of her patients and others.
One client of hers told KIRO 7 News that Danner saved her life after she was recovering from a shoulder surgery, helping her through a very difficult time.
“Harmony believed in me. She never gave up on me. Her intuition for healing and helping and compassion is something you rarely see in a human being. I was blessed to have her as my physical therapist,” she told KIRO 7 News.
Neighbors told KIRO 7 News that Danner was Williams’ wife.
Police said there were no signs of forced entry at the Issaquah home and no outstanding suspects.
In a statement provided to KIRO 7 News, Danielle’s family said: “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.”
Danielle’s executor of estate, Geoff Graves, also released a statement emphasizing her role as Nick’s caregiver and condemning the violence.
“These deaths are unimaginably tragic,” the statement read in part. “Taking another’s life — in this case the lives of a loving mother and her beautiful son — is never a normal response to anger, and we struggle to try to grasp why it had to happen this way.”
Court records provide additional background leading up to the shootings.
Filings in King County Superior Court show that, in the weeks before the deaths, the Mercer Island home was at the center of a contentious vulnerable adult protection order case involving close family members.
The court documents describe Nick Cuvillier as a severely disabled adult with Angelman syndrome, a rare genetic condition that causes developmental delays, limited speech, impaired coordination and a need for near-constant supervision.
Records state he required help with basic daily tasks such as feeding, hygiene and mobility and had lived with family caregivers throughout his life.
In late January, Danielle Cuvillier petitioned the court for a protection order against her son Williams following an alleged assault on Jan. 16.
The petition alleged exploitation, aggressive behavior and improper removal of Nick from her home and requested restrictions on contact and a court-ordered surrender of firearms.
Williams filed a sworn declaration disputing those claims.
In his filing, he described a shared caregiving arrangement that began after their father’s death in 2018 and said he grew increasingly concerned about Nick’s physical injuries, stress-related behaviors and access to medical care while living with their mother.
Williams’ declaration alleges a pattern of physical, verbal and emotional abuse toward Nick over several years, along with concerns about alcohol use and delayed medical treatment.
He said those concerns escalated in late 2024 and early 2025, culminating in a confrontation at the Mercer Island home on Jan. 16.
According to the declaration, Williams went to the home that morning to check on Nick after a scheduled visit was abruptly canceled.
He stated his mother initially refused to let him enter or see his brother and that he called 911 to request a welfare check.
Police responded, and Danielle Cuvillier was arrested on suspicion of domestic violence and released the following day.
Williams said he took Nick with him when he left the home that day and sought medical treatment for injuries he said he sustained during the incident.
Court filings show that Nick lived with Williams and his wife from Jan. 16 through Jan. 30, during which Williams stated Nick’s physical condition and stress-related behaviors improved.
Adult Protective Services opened an investigation during that time, according to the documents.
On Jan. 30, Issaquah police returned Nick to Danielle Cuvillier.
Williams later reported that Nick had expressed a desire to live with him and had signed a durable power of attorney granting him authority over his affairs.
Williams fought for access to Nick at many court appearances in Mercer Island and King County Superior Court.
In one appearance, after a King County judge ruled against him, Williams said, “I think that I showed in my evidence here that my mother is acting in bad faith, and she’s trying to use the court as a weapon to control my brother.”
Court orders also show Williams was served with a temporary protection order requiring the surrender of firearms.
Records indicate he surrendered 53 firearms.
The case remained unresolved at the time of the deaths, and no final rulings had been made regarding long-term caregiving arrangements, guardianship or contact restrictions.
Neighbors in Issaquah described a heavy police response after the welfare check.
“The police came and kicked down their door,” Shelby Rosales said. “They put red tape up and I was like, ‘Oh my god, are my neighbors okay?’”
“They were always kind, considerate neighbors,” Rosales said. “But people have lives that we don’t know about.”
Police have not said whether the court case directly led to the shootings and have emphasized that the circumstances remain under investigation.
Anyone experiencing a mental health crisis or concerns about domestic or family violence is encouraged to seek help through local crisis services or by calling 988, the Suicide and Crisis Lifeline.
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