A 15-year-old boy was charged Thursday with murder in the shooting deaths of his parents and three of his siblings at a home in Fall City, Washington, according to court documents obtained by CBS News.

The teen, whose name is being withheld because he is a juvenile, was charged with five counts of aggravated murder in the slayings of his parents, Mark and Sarah Humiston, two brothers, ages 9 and 13, and his 7-year-old sister, per King County court records.  

He was also charged with one count of attempted murder for shooting and wounding his 11-year-old sister, the documents read.

That girl was in “satisfactory condition” at Harborview Medical Center in Seattle, hospital spokesperson Susan Gregg told the Associated Press Tuesday.

Autopsies performed by the King County Medical Examiner’s Office determined that all five victims died of gunshot wounds. The handgun used in the shooting was believed to belong to the victim’s father, the court records state.

According to the charging documents, just before 5 a.m. Monday, the suspect called 911 with a false story in which he claimed that his 13-year-old brother “just shot my whole family and committed suicide too” at the family’s home in Fall City, which is a community located near Seattle.

However, at about the same time as that call, 911 dispatchers received a second call from a neighbor who lives about a quarter-mile away. That neighbor said the suspect’s 11-year-old sister had ran to his house and was bleeding from what appeared to be a gunshot wound, the documents said.

The girl said her entire family had been fatally shot and identified her 15-year-old brother as the shooter. The girl told dispatchers she was also shot by her brother and “then described holding her breath and playing dead,” the documents read. The girl later told detectives that she had escaped through a bedroom window.

Deputies responded to the Humiston home, where they found the suspect in the driveway and took him into custody, court records show. The five victims were found dead inside the home.

In a hospital interview with detectives later that day, the suspect’s surviving sister said that she identified the firearm used in the shooting as “her father’s silver Glock handgun,” court documents state.

She said that her father kept the pistol in a small lockbox that “he would sometimes put by the front door so he could bring it to work,” the documents read. She told detectives that the suspect was “the only one who knew the combination to the Glock lockbox.”

Investigators determined that the suspect “systematically murdered” his parents and siblings and “then staged the scene prior to the arrival of first responders to make it appear” that the murders had been committed by his 11-year-old brother, documents read. 

The court documents did not speculate on a motive.  

The suspect is scheduled to be arraigned Friday afternoon. The King County Prosecuting Attorney’s Office said in a news release Thursday that the suspect is in custody at the Clark Child and Family Justice Center, which is a juvenile facility.

The teen is currently being charged as a juvenile, and prosecutors said a judge will determine whether his case “will be moved to adult court.” Prosecutors, however, noted that moving the case to adult court does not necessarily mean the suspect would be tried as an adult because, under Washington state law, sentencing guidelines are different for juveniles even if they are tried in adult court. 

In a statement Tuesday, public defenders representing the suspect said that “our client is a 15-year-old boy who enjoys mountain biking and fishing and has no criminal history.”