The 11-year-old who survived a mass shooting inside her family’s ritzy mansion in Washington state said she woke up to the deafening sound of gunshots just before her older brother barged into her bedroom and allegedly opened fire.

The young girl said she pretended to be dead — closing her eyes and holding her breath — after she was shot in the hand and neck out of fear her brother would return to finish the job, according to charging documents released by the King County Prosecuting Attorney’s Office.

She told police her 15-year-old brother used her father’s silver handgun to shoot her parents, Mark and Sarah Humiston, her two brothers and sister to death Monday morning, suspecting his murderous rage came after he failed some tests at school and got into “ a lot of trouble,” according to the emotional recap.

Prosecutors charged the alleged teenage gunman — who was not identified due to his age — on Thursday with five counts of first-degree aggravated murder and one count of first-degree attempted murder.

The lone survivor tearfully recalled waking up during the gunfire and peeking out her bedroom door to see her father and her 13-year-old brother lying dead in a pool of blood in the hallway, the charging docs state.

Their 6-year-old sister — with whom she shared a room — was shot dead as she walked out of their bedroom and into the hallway after she woke up.

After her brother, who was wearing a checkered shirt, allegedly shot her twice, he then left the room and leaned over the three lifeless bodies in the hall to touch their necks and chests to “see if they were alive,” she recalled witnessing.

The youngster then “pretended to play dead” when he re-entered the room and stood next to her bed, according to the charging docs.

The girl escaped through her bedroom window and ran to a neighbor’s house when she heard her brother leave the room and make a phone call, she told police, explaining that the accused teen was the only child who knew the combination to their father’s firearm lockbox.

She was taken to Harborview Medical Center after the horrific slaughter and released on Wednesday.

Prosecutors said the teenage gunman “systematically murdered” his father, mother, two brothers and sister, and attempted to murder his 11-year-old sister. He then staged the bloody scene before first responders arrived in an attempt to pin the killings on his dead 13-year-old brother, who was shot several times in the head, according to the charging documents.

Deputies responded to the Lake Alice Road home — a stunning waterfront property — around 5 a.m. on Monday after receiving a 911 call from the alleged assassin, who claimed his younger brother killed his family and then committed suicide out of fear of being caught viewing pornography.

At the same time, police received an emergency call from a neighbor who reported the 11-year-old survivor was shot and bleeding from the neck and hand. The injured girl then identified her 15-year-old brother as the shooter.

Deputies then found the lifeless bodies of the parents — Mark and Sarah Humiston— and the young victims, inside the Fall City house, prosecutors said, and immediately took the juvenile into custody.

The King County Medical Examiner ruled each death a homicide, according to the charging docs.

The 15-year-old is being held in secure detention at the Clark Child and Family Justice Center in Seattle.

He is due back in court on Friday.