Appearing distressed and aggressive, teenager Zac Erin Barnes walked into the bush and vanished more than six years ago with his family still left wondering what happened.
The 18-year-old asked to get out of a friend's vehicle at night on November 13, 2016 wearing only a faded blue T-shirt, blue shorts and work boots.
He walked off into the dark bushland near the Hunter Valley town of Thornton in NSW and has not been seen by friends, family or anyone else since.
An inquest into what happened to Mr Barnes began on Monday with counsel assisting Tim Hammond saying the teen had not used his bank accounts, social media, phone or government agencies like Centrelink since he disappeared.
"It must be concluded that Zac has passed away," he told Lidcombe Coroners Court.
The three-day inquest will examine events prior to November 13 and how NSW Police handled its investigation after he was reported missing by his mother and stepfather Karen and Michael Gudelj the following day.
The Gudeljs appeared in court alongside some of Mr Barnes' siblings as they seek answers as to the fate of their much beloved family member.
"The circumstances of Zac's disappearance are very sad and the uncertainty of his whereabouts is a hole that remains with his family and friends and never leaves," said Mr Hammond.
In the days before he disappeared, Mr Barnes lost his job after an altercation at work, had to ask for $1200 from his parents partly to repay a debt he owed, and was seen by friends as emotional and crying, drinking more heavily and looking "scattered" and not himself.
"All I have to do is walk into the bush and take a number of pills and no one will ever find me," he allegedly was heard saying after he was fired.
He told another witness that he'd "f***ed everything anyway".
In a Snapchat message, Mr Barnes sent one word, "Dead", to a friend days before he walked into the bush, refusing to disclose where he was.
He was eventually tracked down by that same friend after concerns were raised by Mrs Gudelj.
Saying he didn't want his mother to see him in that condition, he took a ride in another friend's car, eventually becoming aggressive, striking the passenger seat and asking to get out before walking towards the bush.
"Zac was not heard from again that night or since," Mr Hammond said.
In an investigation that spanned years, police divers trawled through nearby dams, searches by land and air were conducted, and police dogs were called in to search for the missing teen.
A tip-off also led investigators to examine a nearby well for clothing or human remains.
Nothing was ever uncovered.
Coroner Carmel Forbes heard Mr Barnes was an exceptional mathematician and a talented footballer at his high school and was working as an apprentice bricklayer when he vanished.
The teen was described as gregarious, boisterous, caring and well-liked.
The officer-in-charge of the investigation, Detective Senior Constable Christopher Walker gave evidence Monday about the searches that police undertook.
Ms Forbes has been tasked with determining the time, date and cause of Mr Barnes' suspected death.
She can also make recommendations regarding steps which should have taken place before and after his disappearance.
The inquest continues on Tuesday.
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