A 15-year-old boy accused of killing his parents and three siblings in a picturesque, $1.4 million lakeside mansion in the Pacific Northwest may be tried as an adult under a move that would result in harsher penalties if found guilty. The Humiston family were horrifically massacred with the boy's father's Glock handgun in Washington last October. The accused teen killer is currently being tried in juvenile court with five counts of first-degree aggravated murder for allegedly killing his parents, Mark, 43, and Sarah Humiston, 42, and three of their children: Katheryn, 7, Joshua, 9, and Benjamin, 13. He is also facing one count of first-degree attempted murder of his surviving sister, 11. A King County Superior Court judge held a hearing on Tuesday as part of the push by prosecutors to determine if the boy will be tried as an adult, The Seattle Times reported. The prosecution requested a 'decline hearing' to begin a long investigation into the boy's life, including his school success, mental health history, or previous disciplinary actions or criminal activity. Judge Veronica Galván said: 'I understand that there's still some investigation, but the factors in the decline hearing are not all tied within some of the things that remain to investigate.' 'So I want to make sure that we are not conflating the two.' Prosecuting attorney Jason Brookhyser said a 'first round' of DNA analysis had been completed, ballistics analysis of shell casings is ongoing, and additional evidence was being tested for DNA. Brookhyser added that they're also waiting on a crime scene response report from the Washington State Patrol, but that they are ready to set a date for the hearing. The boy's defense attorney Kristen Gestaut requested additional evidence before addressing the juvenile decline factors, the outlet reported. Judge Galván ordered the defense to file a brief addressing the factors by next month. But Gestaut argued that 'initial testing' showed 'contamination' of the firearms in evidence for the case. She added that records for the boy's school and medical records were 'very limited' and it has been a challenge to obtain any information from other family members. The next hearing on the decision will be held in September. The two parents and three of their children were found dead, and another injured, just before 5am on October 21 in Fall City, about 25 miles east of Seattle. Mark and Sarah Humiston were said to have been extremely religious and imposed a highly-controlled existence on their five homeschooled children - including dictating who they could be friends with. A police report obtained by DailyMail.com alleged that the teen tried to blame the massacre on his younger 13-year-old brother Benjamin. He claimed Benjamin shot the family and then killed himself after being caught watching porn the night prior to the incident. But it was the 15-year-old's younger sister and sole survivor of the bloodbath that said it was her eldest brother who fired two shots at her. The 11-year-old girl suffered a gunshot wound to the neck and arm but managed to survive the attack by playing dead before escaping through a window and running to a neighbor's home for help, according to an affidavit from the King's County Sheriff. 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 notes that a black Glock pistol had been placed in the child’s hand, but forensic investigators found that the ballistics didn't align with the scene as blood splatter from a fatal wound to the boy’s face was in the wrong place. Neighbors had described the Humistons as 'the perfect family.' Soccer coach Rhea Robertson, who had mentored one of the victims, told KOMO News at a vigil held on Tuesday night that the couple had been 'dedicated' parents. 'Dad worked so hard, and mom was the most dedicated, loyal mother you could ask for,' she said. 'You thought they were perfect. From the outside, they looked perfect to me.' But family insiders told DailyMail.com that their idyllic existence had a dark side, with the ultra-religious parents imposing a strict schedule on their five children and having extremely 'high expectations' of them. The source described how the family maintained a small tight-knit circle and had caused some bad feeling in the community over the summer after ordering their eldest sons to stay away from the children of LGBTQ families living nearby. 'It caused some disquiet,' the source said. 'Mark found out that the boys had made friends with those kids and insisted they didn't see them again. Everyone was quite upset about it.' Yet, a memorial of flowers was placed outside of their home the week of the deadly shooting.