SEATTLE — (AP) — A 15-year-old boy accused of killing his parents and three of his siblings this week east of Seattle tried to pin the slayings on his younger brother, but a sister who survived after playing dead escaped to a neighbor's house and told police who really carried out the shootings, authorities said in a court document made public Thursday.

The boy was charged Thursday in juvenile court with five counts of aggravated murder. Under Washington state law, a hearing is required before the case can be moved into adult court.

The 11-year-old sister who survived Monday's shooting told investigators that the defendant had recently gotten into trouble for failing tests at school, and that the handgun he used belonged to their father. Of all the children, she said, he was the only one who knew the code to the lock box their dad kept it in.

The King County Medical Examiner's Office identified the victims as Sarah Humiston, 42, Mark Humiston, 43, and their children Katheryn Humiston, 7, Joshua Humiston, 9, and Benjamin Humiston, 13.

According to an affidavit of probable cause by King County sheriff's detective Aaron Thompson, the defendant called 911 around 5 a.m. Monday to report that his 13-year-old brother had shot and killed their family at their home in Fall City because he had gotten in trouble for looking at pornography.

A neighbor a few minutes later called 911 saying the injured 11-year-old had come to the home reporting that her family had been shot by her 15-year-old brother and that she had played dead before escaping, the affidavit said.

Arriving deputies detained the 15-year-old in the driveway and found the bodies inside. The 11-year-old was treated at a hospital in Seattle and has since been released, a hospital spokesperson said.

The 15-year-old waived his right to appear in court on Tuesday, according to the King County Prosecuting Attorney's Office. His defense attorneys said in court that he has no criminal history. His attorneys didn't immediately respond to a message seeking comment on the charges Thursday.

The teen is scheduled to appear in court on Friday afternoon.

Mark Humiston worked as an electrical engineer with Hargis Engineers in Seattle.

“We are blindsided and saddened by the tragic events that have led to the loss of a respected colleague, mentor, and friend, as well as the loss of immediate family members," the company said in statement Thursday. "Mark’s leadership and vision were integral within our firm, and he will be greatly missed.”

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