A violent NSW prisoner who said he was going to "kill them all" minutes before suffocating a fellow inmate has been found guilty of manslaughter, not murder, after a judge found he was intoxicated at the time.
Mervyn Keith Davidson was on remand for several violent offences in February 2018, when he walked into 54-year-old Alfredo Pengue's cell at Silverwater prison, shut the door and strangled him.
Shortly before the killing, Davidson consumed ice and Xanax and told other prisoners with his fists above his head that he would "kill them all" .
Two days later during a police interview, he urged police to hurry up.
"I know what I'm here for. Just hurry up and do the charge paperwork so I can go back to my cell and sleep," he said on February 11, 2018.
But Supreme Court Justice David Davies on Wednesday expressed serious doubt the prisoner had the capacity to form the required intent for murder.
Though he rejected Davidson's murder defence of mental illness, the judge said he couldn't find the 46-year-old guilty of murder and instead returned a guilty verdict for manslaughter.
Justice Davies said he couldn't place much significance on the "kill them all" statement due to Davidson's level of self-induced intoxication at the time.
"What was said, accompanied by the clenched fists above the head, only tends to emphasise that the accused was not acting rationally," Justice Davies said.
Two medical experts later diagnosed Davidson with schizophrenia, with one suggesting the inmate's long history of ice use may have caused the disorder to previously be labelled as drug-induced psychosis.
He had reported previous occasions of hearing voices emitting from televisions and radio telling him to do bad things, Justice Davies said.
Pengue was found by another inmate on the ground with blood dripping from his mouth, a swollen right eye and his head almost purple upwards from a horizontal mark on his neck.
At the time of the killing, Davidson was awaiting sentence for attacking a female Aldi worker with a baseball bat during a botched supermarket robbery in the Illawarra region in January 2017.
While in custody for that matter, he punched a police officer and choked his Silverwater cellmate with a t-shirt until the man became unconscious.
Davidson, who was housed in his own cell after that attack, consumed ice weekly in custody in the lead-up to the killing.
He will be sentenced at a later date.