Key Takeaways
- An email sent by Mackenzie "Mack" Williams, 45, three hours before the bodies were found, hinted at a traumatic event and gave clues about his life ending.
- Williams is suspected to have shot and killed three family members, including his wife, younger brother, and mother, before turning the gun on himself.
- A custody battle over Williams’ disabled younger brother, who has Angelman syndrome, may have played a role in the motive behind the shootings.
- Williams had a history of mental instability and unpredictable behavior, and had previously turned over 53 firearms to the police due to a protection order filed by his mother.
- The protection order was dropped approximately three weeks before the shootings, and Williams had been unemployed for several months.
Introduction to the Tragic Event
An email sent by Mackenzie "Mack" Williams, 45, to his friends three hours before the bodies were found, gave clues that his life was about to end. The email, which was obtained by KING 5, appeared to foreshadow the tragic event that would unfold. In the email, Williams wrote about his gun collection and warned his friends that they might encounter something traumatic if they tried to retrieve his weapons. He also stated that his interest was concluded and bid his friends farewell, saying "Sorry to part on these terms. Good luck."
The Discovery of the Bodies
On December 30, 2025, police discovered the bodies of four family members in two separate homes, one on Mercer Island and the other in Issaquah. The first discovery was made at around 10:45 a.m. at the home of Williams’ mother, Danielle Cuvillier, where both she and Williams were found dead from gunshot wounds. Preliminary information led police to believe that the incident was a homicide, followed by a suicide. Shortly thereafter, officers conducted a welfare check at Williams’ home in Issaquah, where they found the bodies of his wife, Harmony Danner, and his disabled younger brother, Dominick "Nick" Cuvillier.
The Investigation and Motive
Multiple sources confirm that police believe Williams shot and killed his wife and brother in Issaquah, then killed his mother in her home on Mercer Island, before shooting and killing himself. However, the motive behind the shootings is still unclear, and the email sent by Williams did not reveal any insight into his reasons. Court records show that Williams had a history of mental instability and unpredictable behavior, and had previously been involved in a custody battle over his younger brother, who has Angelman syndrome. The protection order filed by his mother, Danielle Cuvillier, had been dropped approximately three weeks before the shootings, and Williams had been unemployed for several months.
Family History and Custody Battle
The custody battle over Williams’ younger brother, Nick, may have played a role in the motive behind the shootings. Court records reveal that Williams and his mother had a tumultuous relationship, with Williams expressing concerns about his mother’s mental stability and behavior. In 2025, Williams contacted Adult Protective Services and requested custody of Nick, who stayed with Williams and his wife for about two weeks. The incident that led to Williams requesting custody was a verbal and physical confrontation between him and his mother, which resulted in his mother being charged with fourth-degree assault. Williams had also previously turned over 53 firearms to the police due to a protection order filed by his mother.
Conclusion and Available Resources
The tragic event that unfolded on December 30, 2025, has left many questions unanswered, and the motive behind the shootings is still unclear. However, it is clear that Williams had a history of mental instability and unpredictable behavior, and that the custody battle over his younger brother may have played a role in the events that led to the shootings. If you or someone you know is in crisis, help is available. You can call or text 988 or chat at 988lifeline.org. Additionally, Vibrant Emotional Health’s Safe Space provides digital resources for those in need. KING 5’s Dalton Day contributed information to this story, and the investigation is ongoing.