Prosecutors in Washington accused a 15-year-old boy in the crimes of his parents and three brothers in a house in an affluent neighborhood outside Seattle.

The suspect faces five counts of first-degree murder and one count of attempted murder in connection with Monday’s disturbance in the unincorporated community of Fall City, according to the King County Prosecutor’s Office.

His parents, Mark and Sarah Humiston, as well as three of his siblings — ages 7, 9 and 13 — were found dead at the scene when deputies arrived.

An 11-year-old girl, who is one of the suspect’s two younger sisters, was injured in the shooting and has since been released from a Seattle-area hospital. She managed to escape by playing dead before running to a neighbor’s house for help, according to an arrest affidavit filed in Washington Superior Court for King County.

The gunman was arrested at the scene and has since been held at a juvenile detention center. At a court hearing Tuesday, he waived his right to appear and a judge found probable cause to hold him on five counts of murder and one count of attempted murder. Law enforcement officials and his attorneys said he has no criminal record.

The prosecutor’s office said it would request the case be moved from juvenile court to adult court. If convicted in juvenile court, the teenager could only be held until the age of 25, prosecutors said. If convicted by an adult court, he could be sentenced to 25 years to life, with the legal presumption of release after 25 years.

Molly Campera and Amy Parker, attorneys representing the suspect, did not immediately respond to a request for comment on the charges, which were filed Thursday. After the initial juvenile court hearing, they released a statement reiterating that their client has no criminal record. They described him as a teenager who enjoys mountain biking and fishing.

“The law says our client is presumed innocent of these charges, and we are grateful for a judicial process that requires proof and evidence before there is a ruling,” the statement read.

Teen shot parents, siblings and tried to frame brother, records say

The first call to report the shooting was from the suspect himself, according to an arrest affidavit. Shortly before 5 a.m., the teenager called 911 and told the dispatcher that the 13-year-old brother “just shot my whole family and killed himself,” it said.

Investigators said evidence suggests the suspect shot his parents and siblings and then manipulated the scene so he could blame his brother.

“It appears that (the suspect) systematically killed his mother, father, two brothers and sister and attempted to kill his other sister,” an arrest affidavit said. He “staged the scene before first responders arrived to make it appear that (his brother) committed the murders and then killed himself.”

In an interview with investigators, the 11-year-old girl said she woke up to the sound of a gunshot and saw one of her brothers and her father lying in the hallway, the affidavit states. She told law enforcement she saw the suspect shoot her sister.

The suspect then went into her bedroom and shot her at least once, according to the affidavit. She closed her eyes and held her breath for a while until the suspect left the room. She was able to escape the home through a bedroom window and ran to a neighbor’s house, who called 911.

The 11-year-old said she recognized the gun “as her father’s silver Glock,” the affidavit said. She told police her father kept the gun in a small box, occasionally kept by the front door, so he could bring it to work. She added that of all four children, the suspect was “the only one who knew the combination” to the lock box.

A black Glock handgun was found at the scene, according to the affidavit.

When investigators asked her what problems the suspect had been having at home, she told them “recently he got into ‘a lot of trouble’ for failing some tests at school.”

Father was an engineer, mother was a nurse

Mark Humiston was an electrical engineer for Seattle-based consulting firm Hargis Engineers, where he had a reputation as a mentor who brought leadership and vision to the company, company spokesman Chris Sheldon said in an email to USA TODAY.

“We are blindsided and saddened by the tragic events that have resulted in the loss of a respected colleague, mentor and friend, as well as close family members,” the company said in a statement.

Sarah Humiston held a license as a registered nurse, according to her Washington State Department of Health website. Public records show her license expired in 2022.

Mourners gathered at Fall City United Methodist Church Tuesday night to mourn the Humistons and their children. Local residents who knew the couple and their children said they were a seemingly happy family, well known in the community.

“They were very strong Christians. They loved God. You could tell,” neighbor Camille Sharp said KOMO News. “It’s one of those cliché things everyone says in the news, ‘You’d never guess it,’ and it’s true.”

This story has been updated to include new information

Contribute: Eric Lagatta and Jonathan Limehouse

This article originally appeared on USA TODAY: Washington shooting: Teen accused of killing parents, 3 siblings