Liam Knight's attacker jailed for throwing javelin that pierced his skull

A teenage gatecrasher who threw a steel bar at partygoer Liam Knight, piercing his skull and causing lifelong brain damage, has been jailed for at least eight years.

The youth, known for legal reasons only as DS because he was 16 at the time, threw four steel three-metre bars "javelin-style" from the roof of a shed at a house on Sydney's northern beaches at a backyard birthday party on January 11, 2013.

A number of people, including Mr Knight, then 17, were injured.

'My walking stick is a constant reminder of what I've lost': Liam Knight. Photo: Lidia Nikonova

'My walking stick is a constant reminder of what I've lost': Liam Knight. Photo: Lidia Nikonova

On Friday, acting District Court Judge Ronald Solomon sentenced DS to at least eight years in jail, with a maximum of 12 years and six months, for a string of offences committed that night.

He will remain in juvenile detention until his 21st birthday and then be transferred to an adult prison.

DS was already on bail and on a good behaviour bond for various assault and resisting arrest charges.

In gatecrashing the party, he was in breach of his bail conditions, which included a curfew and non-association order.

Mr Knight – who survived the attack but continues to suffer from epilepsy, loss of motor function and permanent cognitive impairments, and who uses a walking stick – was in court for the sentence, supported by his parents and brothers.

Judge Solomon said DS's actions had had "catastrophic" and "tragic" consequences for Liam, his family and many of the guests who saw the attack.

DS had consumed 20 drinks and ecstasy before unleashing the violence.

During the trial, the District Court heard that, some time before 11pm on January 11, 2013, DS, Jimmy Angelo Tupou and three others arrived at the Staples family's house in Forestville only to be told they were not on the guest list for Harry Staples' 18th birthday party and were not welcome.

DS jumped a fence and shouted to his friends: "Come on, we can come through this way."

Harry Staples' father, Phillip Staples, shone a torch on the youth and said: "Mate, you're not invited, you have to leave."

DS swore at Mr Staples, pushed him on the chest, and then punched one of the party guests in the face.

DS then climbed on to the roof of the shed in the corner of the yard and began throwing building materials that were piled up there.

The court heard that a three-metre steel bar generally used to reinforce concrete struck Mr Knight on the right hand side of the head, piercing his skull and going out the other side.

Paramedics sedated the young man, but had to wait for firefighters to arrive before taking him to hospital so the large piece of steel protruding from his head could be cut.

A few hours later, the teenager had an emergency bilateral craniectomy at Royal North Shore Hospital.

DS had pleaded guilty to recklessly inflicting grievous bodily harm but the Crown did not accept the plea and pressed ahead with the more serious charge of intent, which Judge Solomon, sitting without a jury, found had been proved.

DS also pleaded guilty to a string of violent incidents on the same night, including the assault of Phillip Staples.

In sentencing DS, Judge Solomon said he had begun abusing drugs and alcohol at the age of 15, had a history of truancy and a fractured relationship with his father.

However, he said both DS and the wider community needed to be sent a message that "gatecrashing and violence against guests will not be tolerated".

A Juvenile Justice report said DS had expressed remorse for his actions but has had seven disciplinary incidents while on remand, leading Judge Solomon unable to say he was not at risk of reoffending once he was released from jail.

DS will be eligible for parole on January 14, 2021.

Outside the court, Mr Knight said: "It's been a really long and difficult part of my life and I'm just glad to move on.

"I just want to ensure that all this unprovoked violence is sorted and that everyone realises there's no real point to it.

"There's no winners in this whole thing."

SMH

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