Billy Krey was four years old when he began 'stabbing motions' and the knives were hidden away.
His blackouts were rare, but one of the last times he experienced 'black mode,' he fatally plunged a knife into his neighbour, the NSW Supreme Court was told on Wednesday.
At 19, Krey followed and stabbed father-of-seven Ioakima Sini 16 times outside his home in Whalan in Sydney's west, on July 15, 2017.
Billy Krey (pictured) pleaded guilty to manslaughter and was given six years and six months in prison after being deemed substantially impaired by abnormality of the mind
Krey plead guilty to manslaughter and was deemed substantially impaired by abnormality of the mind and sentenced to at least six years and six months in prison by Justice Mark Ierace.
While Mr Sini had engaged with him first 'the offender's response was so disproportionate that I find the attack was unprovoked,' Justice Ierace said.
Krey's childhood of extreme deprivation and significant mental disorders - foetal alcohol syndrome, intermittent explosive disorder and complex post-traumatic stress disorder - contributed to the offence, the judge found.
'Without them, the attack would not have occurred,' Justice Ierace said.
'The attack was explosive, random and inherently lethal in nature.'
Mr Sini's eldest daughter wrote a statement on behalf of her siblings of the profound impact of losing their father.
Krey had been living with his mother when he awoke at 4pm 'in a bad mood or something' he told police soon after the attack.
The 19-year-old stabbed father-of-seven Ioakima Sini (pictured right) 16 times in an attack outside his home in Whalan in Sydney's west
After accusing his mother of stealing $50 and threatening to stab her, she left and briefly spoke to Mr Sini.
He then walked over to Krey still inside the home
