15-year-old accused of killing his Fall City family tried to frame brother, investigators say

Investigators with the King County Sheriff’s Office accuse a 15-year-old juvenile of shooting everyone in his immediate family at their home in Fall City on Monday, killing five of six family members.

Authorities say the teen also attempted to “stage” the scene and blame his 13-year-old brother, telling dispatchers that the younger sibling had fired on others and then committed suicide.

But his account was directly contradicted by his 11-year-old sister, who was wounded but managed to flee and ask neighbors for help. Charging documents said that from her hospital bed at Harborview, the surviving sibling told investigators that her older brother fired a gun at her as she lay in her bunk bed in the early morning hours Monday.

She heard other gunshots and saw the bodies of family members in the hallway outside her bedroom. Investigators later found the bodies of her mother, father, and three siblings ages 7, 9, and 13.

The girl used the “fire window” in her room to escape. She told investigators she recognized the gun her brother carried “as her father’s silver Glock handgun” and said her brother was the only child in their family who knew the combination to the firearm lockbox. Deputies detained the 15-year-old, the oldest of the family's five children, in the driveway.

On Thursday King County prosecutors charged him with five counts of aggravated murder in the first degree. He’s also charged with one count of attempted murder in the first degree. That charge also carries a firearm enhancement. An arraignment is scheduled for Friday.

KUOW is not naming the suspect because of his age. It is not yet determined whether he will be tried in juvenile or adult court.

The court has barred the teen from having any contact with his younger sister, who was released from Harborview on Tuesday.

On Thursday, the King County Medical Examiner confirmed the names and ages of those killed, listing gunshot wounds as the cause of death for all five family members. They included parents Mark Humiston, 43, Sarah Humiston, 42, and children Benjamin, 13, Joshua, 9, and Katheryn, 7.

KUOW is not publishing the name of the surviving sibling, age 11.

Sheriff's Office Detective Aaron Thompson said in the "certification for probable cause" accompanying the charges that based on the evidence it appears the 15-year-old “systematically murdered” his family members, attempted to murder his surviving sister, and “staged the scene prior to the arrival of first responders” to make it appear that his younger brother had committed the murders and then killed himself.

The accused “then further perpetuated the false staging by repeatedly telling the 911 dispatcher” that his younger brother was responsible. Investigators found the gun in the hand of the deceased 13-year-old. Dispatchers received 911 calls from the accused, and shortly after from neighbors at the house where the sister fled.

The Sheriff’s Office said they took the 15-year-old into custody at the home without resistance. At an initial court hearing on Tuesday, his public defense attorney said the juvenile had no previous criminal history.

At that hearing, in which the juvenile waived his right to a first appearance, King County Superior Court Judge Joe Campagna described the allegations as of the "gravest possible seriousness," and ordered the teen to remain in secure juvenile detention.

Prosecutors said they will ask a judge to move this case to adult court. That would allow for a potentially lengthier sentence. If the case remains in juvenile court, the 15-year old could be held only until age 25. If a judge agrees to transfer the case to adult court, according to prosecutors, “the sentence set by state lawmakers is 25 years to life with a presumption of release after 25 years.”

According to a statement from King County prosecutors, “A case can only be moved to adult court with a judge’s approval after hearing from prosecutors and defense. Based on the details in the charging documents, prosecutors are asking a judge for a hearing at which time both parties will present evidence and the judge will make the determination if the 15-year-old will be moved to adult court.”

The teen’s father, Mark Humiston, worked as an electrical engineer for the firm Hargis Engineers. The company issued a statement this week.

"We are blindsided and saddened by the tragic events that have led to the loss of a respected colleague, mentor, and friend, as well as the loss of immediate family members," the statement read. "Mark’s leadership and vision were integral within our firm, and he will be greatly missed. Our thoughts are with his surviving family, friends, and colleagues during this difficult time."

KUOW's Ann Dornfeld contributed reporting for this story.