Pierce County Prosecutor Mark Lindquist had charged Cristobal Arroyo, 15, with first-degree murder and first-degree robbery in the case. Earlier this week, after four days of testimony, Pierce County Superior Court Judge Thomas Larkin granted the prosecutor's motion to try him as an adult.
He will stand trial alongside his brother, Luis Arroyo, 16, who will also be arraigned as an adult on Friday.
"This is a brutal, adult-sized crime that calls for adult-sized accountability," said Lindquist. "Justice and common sense call for the defendants to be tried together as adults."
According to court documents, the victim met Luis Arroyo at the Arroyo residence on June 1, 2012. Luis Arroyo, armed with a knife, attempted to take the victim's marijuana and cash. The victim, identified earlier as Hector Hernandez, resisted and a fight began.
Cristobal Arroyo heard the struggle and saw his older brother fighting over a knife with the victim. He armed himself with a shank and stabbed the victim in the neck and back, court documents say.
The brothers moved the victim into the bathtub to "drain him" as the victim was still alive and making noises. One of the brothers then cut his throat to kill him, according to the case file.
While attempting to clean the crime scene, the boys' mother came home. She found reddish-brown stains on the floor, which they claimed was chili. When she realized it was blood, the brothers claimed that a man had attacked them and they were forced to kill him. She went upstairs and saw a boy laying on a sheet, dead.
Their mother drove to the neighborhood Tacoma Police Department substation to report the crime. Officers responded to the home and found the victim's body, wrapped in a blanket, in a recycling bin in the alley behind the residence.
During a search of the residence, investigators found two BB guns, a knife, a machete, a makeshift stabbing instrument, a baseball bat and trash bags loaded with used cleaning materials. The weapons appeared to be bloodstained.
Police also recovered two notes from the Arroyo residence.
According to court documents, the first note, consistent with Cristobal Arroyo's handwriting, included a checklist with a series of check boxes labeled: "lay out bags, shut her up, hammer her bones, cutting off limbs, cutting off head, cutting open," and "done."
The second note, consistent with Luis Arroyo's handwriting, included: "cut open, shank the stomach, wack (sic) the head, camera set up," court documents show.
Detectives recovered a cell phone at the defendants' home that contained a short video clip showing the victim lying face down in a bathtub. The brothers' voices can be heard in the video, swearing at and taunting the lifeless body.
In statements to police, the defendants admitted that the victim was alive and making noises when they put him in the bathtub. They ran water over the victim and one of them cut his throat, according to court files.
A 7-year-old female relative of the defendants was home at the time of the killing. She told an interviewer that she heard pounding on the stairs, saw a knife, and saw blood on the carpet and on Luis Arroyo's sleeve. The defendants told the girl that the knife and blood were "fake" and set her in front of a television to watch cartoons.
An autopsy revealed that the victim had been stabbed or cut more than 34 times in the head, neck, back, hands, and chest. There were approximately 60 small puncture wounds on the victim's back and his skull was fractured, consistent with having been struck by a baseball bat or a hammer. Some of the wounds were inflicted after death.
Friends say the victim, Hernandez, was a "good kid" with a great sense of humor who liked to play basketball and was respectful to others.