MERCER ISLAND, Wash. — Court records reveal a yearlong family legal dispute over the care of a disabled family member preceded the deaths of four relatives found at homes in Issaquah and Mercer Island this week.

KING 5 has confirmed the identities of all four people who were found dead. All were members of the same family.

The deaths were discovered Tuesday after police responded to welfare checks in both cities.

According to the Mercer Island Police Department, officers responded at about 10:45 a.m. to a welfare check at a single-family home in the 8400 block of SE 46th Street on Mercer Island.

Inside, officers found two people, identified by Mercer Island police as Danielle Cuvillier, about 80, and her adult son, Mackenzie Williams, dead from gunshot wounds. Police have said preliminary information indicates a homicide followed by a suicide and that there is no ongoing threat to the community.

During the Mercer Island investigation, detectives identified concern for another individual who had previously lived at the home. As a precaution, Mercer Island police asked the Issaquah Police Department to conduct a welfare check at a separate residence.

Issaquah officers responded at about 11:37 a.m. to a home in the 400 block of SE Evans Lane, where they found two more people dead.

KING 5 has confirmed they are Harmony Williams, Mackenzie Williams’ wife, and Mackenzie Williams’ younger brother, Dominick “Nick” Cuvillier.

Police said there were no signs of forced entry. The Washington State Patrol Crime Scene Response Team is assisting with the investigation, and the King County Medical Examiner’s Office will determine the official cause and manner of death.

KING 5 has confirmed a direct connection between the Issaquah and Mercer Island deaths.

Court records reviewed by KING 5 show the family had been involved in an escalating legal dispute over the past year related to the care and guardianship of a disabled family member, identified in documents as Nick, who had Angelman syndrome: a rare genetic disorder that left him mostly nonverbal and dependent on assistance for daily living.

The records show multiple family members filed competing legal documents seeking authority over Nick’s care.

About a year before the deaths, the family’s matriarch filed court paperwork seeking a protection order against her older son, citing concerns about his mental stability, unpredictable behavior and access to firearms. In those filings, she wrote that he possessed a significant number of guns and expressed fear for Nick’s safety.

“(Mack) has a significant number of firearms at his house. (Mack’s) behavior has been unpredictable and aggressive lately. (Danielle) is concerned about (Mack’s) access to these firearms given (his) recent behavior.”

Court records show that shortly after the protection order was filed, the son turned over 53 firearms to the Issaquah Police Department.

The protection order was dropped approximately three weeks ago, restoring his access to Nick.

In a sworn declaration filed in King County Superior Court, Mackenzie Williams described an alleged volatile confrontation with his mother in January that he said escalated into physical violence and prompted him to seek custody of his disabled brother.

Williams wrote that as their father’s health declined, his mother “stated several times that she intended to kill Nick and then herself,” prompting Williams and his father to remove the father’s firearms and secure them in Williams’ gun safe. Williams said the statements and his mother’s behavior caused him increasing concern for Nick’s safety.

Williams detailed events from Jan. 16, when he said he arrived for a scheduled visit that resulted in a violent confrontation and subsequent 911 call, audio which KING 5 has obtained and screened for relevance.

According to Mackenzie Williams, police later arrested his mother for investigation of domestic violence after determining she was the aggressor. She was charged with fourth-degree assault in Mercer Island Municipal Court.

Williams said the incident led him to contact Adult Protective Services and pursue custody of Nick, who stayed with Williams and his wife for about two weeks afterward.

Mercer Island police have not said whether any of these court filings are part of their active investigation.

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