New details shed light on why teen killed family in Washington: lawyer

The deranged 15-year-old accused of slaughtering all but one of his family members in their ritzy lakeside Washington mansion was kept isolated from the world and raised under a “rigid, militant survivalist ideology,” his lawyer claims.

Mark and Sarah Humiston drove their future killer son to the heinous crime after hammering him and his siblings with years of religious extremism and government paranoia, according to court documents filed last week.

Prosecutors say their oldest son — whose identity has been kept under wraps — shot his parents, brothers Benjamin, 13, Joshua, 9, and sister Katheryn, 7, in the middle of the night in October. His 11-year-old sister survived the bloodbath by playing dead.

“A common theme that has been expressed amongst extended family, neighbors, and those who knew the Humistons is that the children were isolated from the outside world and did not engage socially with many peers – only a select few families that went to their church and were friends of their family,” the court documents, obtained by KOMO News, said.

“Furthermore, initial reports indicate the home was abusive, tightly controlled, and dominated by extreme religious beliefs.”

The killer and his dead siblings were homeschooled and kept under a “rigid, militant survivalist ideology,” the documents claim.

The Humisons were allegedly deeply paranoid of the government and medical professionals, especially surrounding the COVID-19 vaccine, leading to what the defense team painted as an isolating lifestyle.

They were also all allegedly given access to firearms, including Mark Humiston’s handgun that the teenager used in his attempt to wipe out his entire family.

The revelations were pieced together from nearly 100 interviews with witnesses and family members, many of whom spoke of the killer teen as “kind, respectful, and deeply devoted to his family.”

Even the boy’s maternal grandmother sided with him, telling attorneys that Sarah Humiston “was abusive and demeaning to the children.”

The woman allegedly told cops she had previously threatened to report the Humiston parents if their abuse did not stop.

The alleged abuse apparently came to a head last October when the 15-year-old methodically gunned down his family members one by one in their $2 million suburban Seattle mansion.

The teen opened fire around 5 a.m., chillingly shooting them and then returning to check their pulses.

Only his sister, an 11-year-old, survived by playing dead when he fired at her neck and hand. She slipped out of a window to a neighbor’s house before he could finish the job, police said.

At the same time, the gunman called 911 and told dispatchers that his 13-year-old brother had killed their family and “taken himself out” because he had gotten in trouble looking at pornography the night before.

He then staged the bloody scene before first responders arrived in an attempt to pin the killings on his dead brother, even putting a gun in his hand, according to the charging documents.

The teen was immediately taken into custody and faces five counts of first-degree aggravated murder and one count of first-degree attempted murder.