The disappearance of a young Belgian backpacker in south-east Australia that has confounded authorities for more than three years remains a mystery after the conclusion of an inquest.

A coroner ruled that 18-year-old Theo Hayez likely died soon after he left a nightclub in the coastal town of Byron Bay in New South Wales in May 2019, but she could not say whether it was as a result of an accident or if he was killed by others.

New South Wales state coroner Teresa O’Sullivan said suicide appeared to be highly unlikely and there was no reason for Mr Hayez to intentionally vanish.

But she said she could not make a finding on the two theories put forward at the inquest into his disappearance.

One was that Mr Hayez had a fatal accident as he tried to climb towards the lighthouse at Byron Bay. The other was that one or more people caused his death and disposed of his body.

“Sadly, there is just insufficient evidence before me to substantiate or exclude either theory,” Ms O’Sullivan said.

Jean-Philippe Pector, the godfather of Mr Hayez, told reporters outside the Byron Bay Court House that the family knew there would not be any breakthrough after going through the inquest process, but they remained hopeful the “main question” would one day be answered.

“It’s obviously a really tough moment because it’s the end of a tough process,” Mr Pector said. “But I think it’s best that the case remains open, allowing new evidence to come forward.”

Mr Hayez, who was preparing to return to Belgium after eight months of traveling around Australia, was last seen at about 11pm on May 31 2019, after leaving the Cheeky Monkeys nightclub in Byron Bay.

Police were alerted six days later when he failed to return to his hostel and could not be found nor contacted.

A large-scale search was launched, but the only thing authorities found was a hat they believed was owned by Mr Hayez.

Police in February announced a 500,000 Australian dollar (£278,000) reward for anyone with information about the case.

The coroner said: “I hope if there is any further information to be known, the reward would provide a motivation to come forward and contact CrimeStoppers.”

Ms O’Sullivan acknowledged the sadness and loss experienced by the family and friends of Mr Hayez, some of whom had travelled from Belgium to Byron Bay for the inquest.

“It is obvious from the evidence he had a bright future ahead of him,” she said.

Mr Hayez’s cousin Lisa Hayez told reporters that Byron Bay felt like the worst place in the world, but also somehow like home.

“Like I was telling JP (Pector) driving here, I feel like I’m driving home, like I’m going home to my people,” she said. “It’s very, very special and really hard to describe.”