Prosecutors cite alleged planning and an effort to blame a dead sibling, while the defense emphasizes youth, mental illness and rehabilitation.
SEATTLE — Nearly two years after five members of a Fall City family were shot to death, a King County judge has begun hearing evidence on a question that will shape the rest of the case: whether the teenager accused in the killings should be prosecuted as an adult.
The proceeding, known in Washington as a decline hearing, began Tuesday before Judge Veronica Galvan. Prosecutors are asking the court to give up juvenile jurisdiction over the defendant, who was 15 at the time of the October 2024 shootings and is now 17. His lawyers want the case to remain in juvenile court, where treatment and rehabilitation carry greater weight and the available sanctions differ sharply from those in adult criminal court.
The state opened by emphasizing what prosecutors describe as a deliberate sequence of killings followed by steps intended to conceal what happened. The teenager is accused of killing his parents, Mark and Sarah Humiston, and three siblings at the family’s home in Fall City on Oct. 21, 2024. A fourth sibling, an 11-year-old girl at the time, was wounded but survived and escaped to a neighbor’s home.
Prosecutors say the surviving girl identified her older brother as the shooter. Investigators also allege he tried to shift blame to his 13-year-old brother, Benjamin, who was among those killed. Court records from the original investigation say the defendant called 911 and reported that Benjamin had killed the family and then himself. Authorities later said the surviving sister’s account and physical evidence did not match that version of events.
Senior Deputy Prosecuting Attorney Jamie Kvistad argued that events after the shootings showed planning and an awareness of what the teenager had done. Prosecutors say he moved the firearm, altered the scene, showered and changed clothes before calling authorities. They also say evidence involving Benjamin’s injuries supported their allegation that the scene had been manipulated to make the younger brother appear responsible.
The five people killed were Mark Humiston, 43; Sarah Humiston, 42; Benjamin Humiston, 13; Joshua Humiston, 9; and Katheryn Humiston, 7. The defendant was arrested after deputies responded to the home. He was charged in juvenile court with five counts of aggravated first-degree murder and one count of attempted first-degree murder. He has remained in juvenile detention while the court case and transfer question have moved forward.
The defense is urging Galvan to consider more than the alleged actions on the morning of the killings. Attorney Amy Parker described a childhood marked by isolation, strict control, alleged physical abuse and limited medical care. The defense says the children were raised with extreme religious and anti-government beliefs and that the defendant’s mental health deteriorated before the deaths. Two psychiatrists working with the defense have diagnosed him with bipolar disorder, Parker told the court.
Defense attorneys are also pointing to the teenager’s conduct while detained. They say he has received regular mental health treatment, helped other youths and largely avoided serious disciplinary problems. That record, combined with his age and psychiatric history, is central to their argument that he remains capable of rehabilitation within the juvenile system. The defense did not use its opening presentation to contest the seriousness of the deaths, instead focusing on what it says preceded the shootings and what has happened since.
Washington law permits a prosecutor, defendant or judge to seek a transfer to adult criminal court in certain serious cases. In a discretionary decline hearing, the court considers reports, facts, expert opinions and arguments before deciding whether transferring the case would be in the best interest of the juvenile or the public. The judge must explain the eventual decision in written findings supported by the evidence presented at the hearing.
The transfer dispute is separate from the ultimate question of criminal guilt. No trial has yet determined the allegations against the teenager. The current hearing instead determines which court will handle that trial and, if there is a conviction, which sentencing structure will apply. Prosecutors contend that the scope of the killings, the number and ages of the victims and the alleged efforts to conceal the crime support adult prosecution. The defense says the teenager’s background, developmental status, mental health and response to treatment support keeping jurisdiction in juvenile court.
The hearing is expected to stretch over several weeks as both sides present testimony and evidence. Galvan, who has overseen the case since its early stages, has not announced a decision. The defendant remains in juvenile detention, and a court order restricts news organizations from showing his face or identifying him by name while the transfer proceedings continue.
Author note: Last updated September 16, 2026.