A 15-year-old boy has been charged with five counts of aggravated murder after his parents and three siblings were shot to death.

The incident occurred at a home east of Seattle in Washington state, and the unnamed defendant allegedly tried to frame his younger brother for the attack.

But her injured 11-year-old sister was said to have survived by playing dead and running away to a neighbor who called police, according to an affidavit of probable cause by King County sheriff’s detective Aaron Thompson.

The victims were identified by the King County Medical Examiner’s Office as 43-year-old Mark Humiston, his wife, 42-year-old Sarah Humiston, and their children, 7-year-old Katheryn Humiston, 9-year-old Joshua Humiston, and 13-year-old Benjamin Humiston.

The 11-year-old sister told investigators that the defendant was in trouble because he had recently failed school exams and that the gun he used belonged to their father.

The unnamed girl added that out of all the children, she was the only one who knew the code to the lock box where the gun was hidden.

Police received a 911 call from the defendant around 5 a.m. Monday, according to the affidavit.

He said his 13-year-old brother shot and killed his parents in Fall City because they got him in trouble for looking at pornography.

But a few minutes later, the neighbor also called 911 and reported what her little sister had told her.

Police arrived at the scene and arrested the 15-year-old boy in the driveway before finding the bodies inside.

The 11-year-old boy was treated in hospital before being discharged.

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The defendant waived his right to appear in court Tuesday, according to the King County Prosecutor’s Office, but his attorneys said he has no criminal history.

He will appear in court Friday afternoon.

Mark Humiston worked as an electrical engineer at Hargis Engineers.

The company said in a statement: “We are stunned and saddened by the tragic events that have led to the loss of a respected colleague, mentor and friend, as well as close family members.

“Mark’s leadership and vision were an integral part of our firm and we will miss him greatly.”