Teenager is charged with murdering five family members in a home in Washington state

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

The teenager, who is not being named because he is a minor, was charged with five counts of aggravated homicide in the murder of his parents, Mark and Sarah Humiston, two brothers ages 9 and 13, and his seven-year-old sister, according to King County court records.

He was also charged with attempted murder for shooting and wounding his 11-year-old sister, according to the documents.

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

Autopsies conducted by the King County Medical Examiner's Office revealed that all five victims died of gunshot wounds. According to court documents, the gun used in the shooting belonged to the victim's father.

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

However, around the same time as that call, emergency 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 ran to his house and appeared to be bleeding from a gunshot wound, documents said.

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

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

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

She said her father kept the gun in a small locker that he “sometimes placed by the front door so he could take it to work,” the documents said. She told investigators that the suspect was “the only one who knew the combination to the Glock locker.”

Investigators determined that the suspect “systematically murdered” his parents and siblings and then “staged the scene before first responders arrived to make it appear” that the murders were committed by his 11-year-old brother, it said the documents.

There was no speculation about a motive in court documents.

The suspect is scheduled to be arraigned Friday afternoon. The King County Prosecutor's Office said in a news release Thursday that the suspect was being held at the Clark Child and Family Justice Center, a juvenile detention center.

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

In a statement Tuesday, the suspect's public defenders said, “Our client is a 15-year-old boy who enjoys mountain biking and fishing and has no criminal record.”