A teenager slit the throat of a stranger while "smiling and laughing", after the attacker's friendly demeanour darkened like "someone shoved crack cocaine up his butt".
After his arrest, Flynn Crowther Donohue cornered an inmate and brutally stabbed him 38 times with a sharpened, broken tennis racquet.
In an ACT Supreme Court decision published on Friday, Justice David Mossop sentenced the teenager to 13-years-and-five-months jail with a six-year non-parole period.
The 19-year-old had pleaded guilty to attempted murder and intentionally inflicting grievous bodily harm.
Donohue had just turned 18 when, in July 2023, he met two strangers at the Woden shops.
He was invited back to the man and woman's unit to drink alcohol, eat food, listen to music, and smoke marijuana.
Donohue's demeanour soon changed from relaxed and friendly, to like "someone shoved crack cocaine up his butt", the published judgment states.
He screamed in the face of the man, punched holes in the wall, and became "quite sexual" towards the woman.
After being told that it was "time for you to fuck off", Donohue came up behind the male victim, grabbed his hair, and held a knife to his throat.
When the man tried to grab the knife, the then-18-year-old slit his throat in one motion while "laughing and smiling".
The woman then started punching Donohue, before she "plugged" the victim's throat with her fingers and called an ambulance.
Donohue left, caught a bus to Manuka McDonald's and unsuccessfully tried to purchase items twice. He was arrested later that day.
The victim was taken to hospital, where he had life-saving surgery and was given eight units of blood. He was sedated for 24 hours and needed a tracheotomy tube for six days.
About five months later, while in custody at the Alexander Maconochie Centre, Donohue repeatedly stabbed another inmate with a sharpened wooden spike made from a broken tennis racquet handle.
The other prisoner suffered 38 wounds to his head, neck, arms, abdomen and back. This included 11 stab wounds to his neck, and six to his head and face resulting in permanent scarring.
In a telephone call to his mother, Donohue said he attacked the inmate because the other man had called him a "dog".
Justice Mossop said the attempted murder involved "attacking an extremely vulnerable part of the body with a knife" and "the likelihood of death was high".
"For somebody so young, the evidence indicates that the offender has a dangerous propensity to resort to violence," the judge stated.
"That appears to be an ingrained part of his personality structure, having difficulty with impulsivity and emotional regulation, combined with significant levels of fear and anxiety. It is a dangerous combination."
Donohue will be eligible for parole in August 2029.
