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Lawyer gives insight into teen's behavior and potential motive for allegedly killing parents and 3 siblings

Home> News> US News

Updated 13:36 2 Aug 2025 GMT+1Published 11:05 2 Aug 2025 GMT+1

Lawyer gives insight into teen's behavior and potential motive for allegedly killing parents and 3 siblings

The 15-year-old reportedly gunned down members of his family

Liv Bridge

Liv Bridge

A lawyer has revealed a potential motive for the teenager who allegedly killed his parents and siblings.

On October 21 last year, Seattle cops were called to reports of gunfire at a residential home in Fall City, Washington, at around 5am.

At the scene, two adults and three youngsters were tragically found gunned down, while a fourth victim, age 11, was found alive with injuries.

Parents, Mark Humiston and his wife, Sarah, were soon identified as the adult victims alongside three of their children, Benjamin, 13, Joshua, nine, and Katheryn, seven.

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It is believed their 11-year-old daughter managed to survive the bloodbath by playing dead.

Meanwhile, the Humiston's 15-year-old son, whose identity has not been published for legal reasons, was arrested at the scene and stands accused of the heinous slayings.

Mark and Sarah Humiston (Facebook)
Mark and Sarah Humiston (Facebook)

Now, his attorney has suggested a potential motive for the teen, claiming that Mark and Sarah kept their children cooped up inside their $2 million lakeside mansion, isolated from the outside world and raised under a 'rigid, militant survivalist ideology'.

According to LinkedIn, Mark, who was originally from Texas, worked as an Associate Principal at Hargis Engineers in Seattle for almost 20 years.

According to court documents filed last week, it is claimed the parents drove the boy to commit the crime after being homeschooled and indoctrinated with years of 'religious extremism' and government paranoia.

It is alleged the children were homeschooled and 'abused' by their parents (KOMO News)
It is alleged the children were homeschooled and 'abused' by their parents (KOMO News)

Based on almost 100 interviews with witnesses and family members, the documents state: “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,” as per KOMO News.

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

It is claimed the Humistons became paranoid by the COVID-19 vaccine and medical professionals.

Mark Humiston was an Associate Principal at Hargis Engineers (LinkedIn)
Mark Humiston was an Associate Principal at Hargis Engineers (LinkedIn)

They also allegedly had access to firearms and a handgun, which is believed to have been used by the teen in his alleged attempt to kill his entire family.

Other witnesses and family members further described the accused as 'kind, respectful and deeply devoted to his family,' including his maternal grandmother who told lawyers that the mom was 'abusive and demeaning to the children'.

The woman also allegedly said she had threatened to report the parents to the cops if the abuse did not stop.

As for the teen, it is claimed he open fired on his family in the early hours, before returning to check their pulses.

The 11-year-old girl suffered injuries to her neck and hand, but managed to flee the scene by escaping out of a window to a neighbor's home.

The couple allegedly raised the children with strict religious beliefs (National Gun Violence Memorial)
The couple allegedly raised the children with strict religious beliefs (National Gun Violence Memorial)

The gunman reportedly called cops himself and told dispatchers that his brother was the one who had murdered the family before 'taking himself out', after getting into trouble looking at pornography the night before.

Before cops arrived, he apparently set up a scene to make it appear his brother was responsible by putting a gun in his hand.

Cops said there was 'no significant confrontation' when they took him into custody from the scene.

The prosecution is arguing the teen is a 'threat to community safety', while the defense state he has 'no criminal history'.

He faces five counts of first-degree aggravated murder and one count of first-degree attempted murder.

Featured Image Credit: Facebook/ Mark Humiston

Topics: Crime, Gun Crime, Religion, US News, Washington, Parenting

Liv Bridge
Liv Bridge

Liv Bridge is a digital journalist who joined the UNILAD team in 2024 after almost three years reporting local news for a Newsquest UK paper, The Oldham Times. She's passionate about health, housing, food and music, especially Oasis...

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@livbridge

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