Shock revelation about the scene of Fall City murder where teen slaughtered family at lakeside mansion

Prosecutors are accusing defense attorneys of altering the crime scene, violating a court order during their investigation of a chilling case in Fall City, Washington, that saw a 15-year-old boy allegedly murder his family. 

The King County Prosecuting Attorneys Office claims the defense team mishandled evidence while conducting an unsupervised search of the home.

The boy, whose identity remains withheld due to a court order, is charged with killing his parents, Mark Humiston, 43, and wife Sarah, 42, along with his younger siblings: Benjamin, 13, Joshua, 9, and Katheryn, 7.

The gruesome murders occurred in the early hours of October 21 at their $2million luxury lakeside mansion on Lake Alice Road Southeast.

The only survivor, an 11-year-old girl, escaped after being shot, seeking refuge at a neighbors house.

According to court documents, the teen allegedly staged the crime scene to implicate his 13-year-old brother. 

He then called 911, claiming his younger sibling had shot the family before turning the gun on himself. 

However, investigators quickly debunked his version of events citing autopsy results and ballistic evidence.

Electrical engineer Mark Humiston, 43, and his registered nurse wife Sarah, 42, were found dead at the home along with three of their children

The teens three siblings, Benjamin, 13, Joshua, 9 and Katheryn, 7, were killed in the shooting. His 11-year-old sister survived 

Last month, on October 28, Judge Veronica Galvan granted a motion allowing the defense team unsupervised access to the home. 

They were permitted a 10-hour window the following day to take photos, conduct 3D scans, and search the boys bedroom.

However, strict conditions were imposed: they could only examine items in plain view and were prohibited from removing or searching through file cabinets, containers, drawers, digital devices, and the like.

But in a motion filed on November 5, Senior Deputy Prosecuting Attorney Jason Brookhyser alleged that the defense violated these terms. 

Prosecutors presented photographic evidence suggesting that items, including a bottle of Clorox wipes and childrens backpacks, had been moved or removed entirely.

It is clear that defense counsel and their agents exceeded the permitted scope of their search under the Courts order, Brookhyser stated in the filing.

The prosecution is now seeking an order compelling the defense to turn over all materials collected during their search. 

They argue the court must have access to this evidence to determine whether the defense acted appropriately.

Lawyers for the 15-year-old boy (pictured) accused of killing his parents and three siblings in Fall City, Washington, claim his brother committed the crime

Prosecutors are accusing defense attorneys of altering the crime scene, violating a court order during their investigation of a chilling case in Fall City, Washington

While the defense is seeking to preserve its ability to argue for its clients innocence, the prosecution remains focused on what they see as a clear violation of trust.

Brookhyser has emphasized the importance of adherence to court orders, noting, The State is entitled to possession of those materials in the due course of counsels reciprocal discovery obligations.

In an earlier motion, defense attorney Amy Parker stated, The States theory is that [15-year-old] was involved in a mass killing of five people with firearms confined to a basement. There is no evidence at this point that we have received that indicates [15-year-old] had any blood on him.

Parker also argued for the importance of unbiased investigations: In my experience, it is beneficial for defense to have an opportunity to investigate the crime scene in this case free from [law enforcement] bias, she wrote.

The couple were extremely religious - imposing a highly-controlled existence on their five kids which included dictating who they could be friends with and homeschooling them

Defense attorneys were permitted a 10-hour window  to take photos, conduct 3D scans, and search the boys bedroom but they are now accused of mishandling evidence

According to detectives, the 15-year-old also attempted to stage the crime scene to lend credence to his story that it had been a murder-suicide perpetrated by Benjamin.

The report noted that a black Glock pistol had been placed in the childs hand but forensic investigators spotted that the weapon hadnt been fired and that blood splatter from a fatal wound to the boys face was in the wrong place.

Despite these assertions, Parker and co-counsel Molly Campera withdrew from the case shortly after the unsupervised search.

The teen is now  being represented by a new attorney, Kristen Gestaut of Obsidian Law Offices.

The prosecution is pushing to move the case to adult court, given the severity of the charges. 

According to investigators, the 11-year-old survivor told detectives she witnessed her brother shooting family members and then checking their pulses to ensure they were dead. 

According to investigators, the 11-year-old survivor told detectives she witnessed her brother shooting family members and then checking their pulses to ensure they were dead

Her older brother then re-entered her bedroom, where she closed her eyes and held her breath as he stood next to her bed.

Once her brother left her room and she could hear him upstairs on the phone, she used the window to escape before running to her neighbors house and incessantly ringing the doorbell - fearing her brother would come to find her.

The surviving daughter, who was bleeding from her neck and hand, told the neighbors that her family was dead at the hands of her own brother before they phoned police.

Additionally, she told how the teen was the only sibling who knew the combination code to the gun safe. 

She played dead before she escaping the bloodbath through a fire window in her room and ran about a quarter of a mile away to a neighbors house. 

In a disturbing detail, she remembered her brother leaning over the three family members he gunned down in the hallway before touching their bloodied bodies to make sure they were actually dead.

Documents obtained by DailyMail.com show the accused shooter attempted to blame the murders on Benjamin, claiming his younger sibling shot the family members and killed himself after being caught watching porn the previous evening.

But autopsy reports further contradicted the teens initial claims. 

Benjamin was shot multiple times, including a fatal shot to the back of his head from more than two feet away.

Police say it was the 15-year-old who massacred nearly his entire family using his fathers Glock handgun, with his younger sister - the only survivor of the bloodbath - saying it was her eldest brother who fired two shots at her, hitting her in the neck and arm.

The teens attorneys insist his murder-suicide theory is forensically viable, according to court documents obtained by The Seattle Times. 

The case continues to unfold as both sides prepare for a legal battle that will determine the teens fate in what has become one of the most disturbing cases in recent memory.