A DEVIL-worshipping teenager had a simple code for a sinister plan - 5455.
Those numbers produce the word "kill" on a telephone keypad - and that's just what the 16-year-old intended to do.
A court yesterday heard details of the teenager's alleged plot to kill his parents, two school friends and then himself - all on the orders of the Devil.
When police arrived at their Baulkham Hills home at 7.15am on March 25, 2008, they found the boy freshly showered and dressed for school - but his father was dead, his mother badly wounded, a 23cm knife was in his bag.
Numerous drawings, text books and exercise books full of handwritten "musings" on Satanism and the afterlife were also found, the Supreme Court heard yesterday.
He has pleaded not guilty to murder and wounding with intent to murder, with the court told he was suffering from a severe mental illness at the time.
Crown prosecutor Peter Miller told the judge-alone trial yesterday that the young man had given clues about his motive as he attacked his parents.
Upon hearing his wife's screams, the youth's father came running down the stairs only to himself be attacked.
The boy's father died from his injuries at the scene.
When the boy went upstairs to change his T-shirt, his mother called emergency services telling them: "My son's going to kill me now." Police were on the doorstep by the time he returned downstairs.
He told paramedics at the scene: "I just murdered my parents," the court was told.
The court was told the boy had an interest in Satanism and had notebooks full of "meditations" on the afterlife.
Psychiatric examinations revealed the boy was delusional and had - on at least three separate occasions - heard what he thought to be the devil's voice, Mr Miller said.
"He had a firmly held belief that he could influence his own afterlife," he said.
The document titled 5455 revealed what appeared to be an even more sinister plot involving the killing of two classmates.
He had even written a suicide note, the court was told.
That plan was scuppered because on the day in question, a week earlier than the attack on his parents, his father had gone to work earlier than expected, Mr Miller said.
Counsel for the youth Andrew Haesler SC said his client had a "disease of the mind" and was suffering from schizophrenia.
The trial before Justice Clifton Hoeben is continuing.