A 15-year-old boy in Washington state is facing five counts of murder and one count of attempted murder after his parents and three siblings were found shot to death in their family home Monday morning.

An 11-year-old sister was also shot, according to court documents, but survived by playing dead and managed to escape through a window and ran to a neighbour’s house, alerting them of the gruesome slayings.

When police responded to several 911 calls that morning, the found two adults and three children – seven, nine and 13 years old – dead at the home in Fall City, approximately 40 kilometres east of Seattle and 260 kilometres from Vancouver, BC.

According to NBC News, the medical examiner’s office identified them as Mark Humiston, 43, Sarah Humiston, 42, and their children Katheryn, 7, Joshua, 9, and Benjamin, 13.

The 15-year-old boy, whom police have identified but a judge has ordered news media not to name, was arrested the same day as the shootings took place and is now being held at a detention facility for juveniles.

The King County Sheriff’s Office said the teen placed a call to them in pre-dawn hours on Monday, trying to falsely pin the shootings on his 13-year-old brother, saying his sibling “just shot my while family and committed suicide, too,” USA Today reports.

Investigators told reporters Thursday that, based on the evidence collected at the crime scene, the suspect shot his parents and siblings before tampering with the scene to try and frame his brother.

“It appears that (the suspect) systematically murdered his mother, father, two brothers, and sister, and attempted to murder his other sister,” an arrest affidavit viewed by USA Today said. “(He) then staged the scene prior to the arrival of first responders to make it appear that (his brother) had committed the murders and then killed himself.”

Neighbours leave the scene of a fatal shooting Monday morning, Oct. 21, 2024, in Fall City, Wash.

Neighbours leave the scene of a fatal shooting Monday morning, Oct. 21, 2024, in Fall City, Wash.

Kevin Clark/The Seattle Times via AP, File

In an interview with investigators, the surviving sister said she was startled awake by the sound of gunshots in the home early Monday morning and found one of her brothers and her father lying in the hallway. She said she then watched her sister get shot.

The suspect then came into her room and shot her, a sheriff’s detective wrote in a probable cause statement. She closed her eyes and tried not to breathe, she said, listening as she heard someone else shout “stop” and “help.”

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Shortly after, she escaped through her bedroom window and fled to the safety of a neighbour’s house.

The surviving sibling told investigators that she recognized the gun used by the suspect as the Glock her father kept in a safe by the home’s main door, which her father sometimes took to work. She said the suspect was the only one of the children who knew the combination.

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

According to NBC, at the first court appearance for the 15-year-old, his lawyers described him as a “boy who enjoys mountain biking and fishing and has no criminal history.”

Bouquets of flowers line a stone picnic table at a roadside park as a small memorial to the victims of a mass shooting the day before in Fall City, Wash., Tuesday, Oct. 22, 2024.

Bouquets of flowers line a stone picnic table at a roadside park as a small memorial to the victims of a mass shooting the day before in Fall City, Wash., Tuesday, Oct. 22, 2024.

Jennifer Buchanan/The Seattle Times via AP

“I would remind everyone that these are not proven facts, merely allegations, and the law presumes our client is innocent of these charges,” Amy Parker and Molly Campera said.

A member of King City council, Sarah Perry, wrote on Facebook asking the community to rally around the family and seek support if needed.

“At this time, I ask you to join me in holding all family members, the community members of Lake Alice and Fall City, as well as all those impacted by this terrible situation, in your heart with prayers of peace and healing,” she wrote.

If found guilty, the suspect could be sentenced in juvenile court to life with a presumption of release after 25 years, the authorities said, according to the New York Times. However, if prosecutors request the boy be tried in an adult court and it’s granted by a judge, a guilty verdict could bring a life sentence without the presumption of release.