Where's Theo?
It is a question that has been asked from Byron Bay to Belgium since the disappearance of 18-year-old backpacker Theo Hayez two and a half years ago.
It is also a puzzle that has left his family lost in a sea of sadness and uncertainty.
Belgian student Theo Hayez was backpacking in Australia when he went missing. His body has never been found Photo: NEW SOUTH WALES POLICE / AFP
Evidence given by Theo's brother Lucas at the close of an inquest this week left Coroner Teresa O'Sullivan weeping, and led her to temporarily adjourn the court.
"Before leaving I had asked him for a jumper with his smell in memory of him waiting for his return," Lucas Hayez said.
"He took me in his arms for the last time saying he was not leaving forever, and he promised me to come back really fast."
Theo Hayez was last seen leaving the Cheeky Monkeys nightclub about 11pm on May 31, 2019.
His disappearance remains a mystery and, with celebrity town Byron Bay in the mix, one that has proven irresistible to the media.
So, after a two-week coronial inquiry, what has been learnt and what remains unknown?
How did Theo find himself alone at 11pm?
Theo was kicked out of the Cheeky Monkeys nightclub because staff thought he was showing signs of intoxication.
But the inquest heard from several backpackers who were with Theo on the night of his disappearance, and none thought he was drunk.
CCTV footage of him in and around the nightclub is inconclusive.
When security staff from the venue gave evidence about their decision, Theo's father Laurent stormed out of the court.
Was Theo lost?
When Theo left the club, he checked his phone for directions back to the Wake Up! hostel where he was staying, but then headed in the opposite direction.
The court heard Theo was an excellent navigator on Google Maps.
His cousin Lisa Hayez said it was common for them to enter directions into Google Maps and then use the map to navigate by zooming in and out without changing the directions.
Was anyone with him?
The Hayez family have repeatedly said they do not believe Theo was alone after he left Cheeky Monkeys.
Belgian authorities were able to use technology called geo-fencing to check for other phones in the same area at the same time.
They ran searches on five key locations, including the cricket nets near the Byron Bay Youth Centre, where digital data shows he spent seven minutes.
No other phones were detected, but the court was told the technique did not work for Apple phones.
Lisa Hayez told the inquest she had walked the secluded path Theo followed and was convinced he would never have embarked on the trek through dense bushland alone.
What happened to Theo's mobile phone?
Theo's phone has never been found, but his family managed to gain access to his Google account, which provided a "digital data trail" of his movements on the night he disappeared.
The last reliable data point places the phone at Cosy Corner on Tallow Beach, at the base of the Cape Byron cliffs.
Police believe Theo sent light-hearted messages to his friends and family in French from that location, with the last message sent to his step-sister Emma at 12:55am.
Counsel Assisting the Coroner, Kirsten Edwards, told the court that just minutes later, at 1.02am, something happened.
"If we knew what that was, we would probably know what happened to Theo," she said.
Theo's phone stopped receiving data from Telstra phone towers, either because it was suddenly out of range or because it was switched off or put into flight mode.
But at 6.17am the phone started receiving data again, meaning it did not go into the water (the manufacturer confirmed it would not receive data if submerged).
The handset remained in roughly the same area, until its battery presumably ran out, but it has never been found.
Mother Vinciane Delforge (left), grandmother Jacqueline Jourquin (second L), and father Laurent Hayez (right) pictured at the start of the Coroner's inquest Photo: BELGA VIA AFP
Was there foul play?
The officer in charge of the investigation, Detective Senior Constable Philip Parker, said "it could be possible" Theo was abducted, but police hadn't "found any information to that regard".
He also said there was nothing that had "come to light during the investigation" to suggest there was any form of foul play or homicide involved.
Was Theo using a dating app to meet someone?
This theory was addressed early on in the inquest.
Counsel Assisting the Coroner told the court "the use of Grindr has also been suggested but we know Theo did not have that app or any like app on his phone."
She also dismissed reports that Theo's phone engaged in some sort of "digital handshake" during his trek to Tallow Beach.
Edwards said there was evidence of a brief connection to an IP address from the Telstra service just before 1am but there was no evidence Theo was near another mobile device at that time.
Could Theo still be alive?
Detective Senior Constable Parker told the inquest he believed Theo was dead because his bank and social media accounts had not been used since he went missing.
Nor had he made contact with family or friends, which was extremely out of character.
Could it have been suicide?
This explanation was ruled out almost immediately at the inquest.
Theo was by all accounts happy and optimistic about life, and excited to start his next chapter studying engineering back in Belgium.
He had made plans to catch up with friends and family on his return, and had no history of mental illness or suicidal ideation.
So, was it death by misadventure?
The working theory of police is that Theo may have been trying to get to the Cape Byron Lighthouse, a popular tourist attraction.
This could explain why he searched for directions to his hostel, to work out exactly where he was, but then travelled in the opposite direction.
Detective Senior Constable Parker told the inquest the bush track Theo used may have appeared on Google Maps as a more suitable route than it actually was.
He said if Theo tried to walk up the "deceptively easy" grassy side of the cliff from Cosy Corner, he may not have realised the other side was steep and unstable shale.
The difficulty with this theory is that it is hard to see any pathway at night and Theo's family feel it would have been completely inconsistent with his character to have attempted such a climb.
If he did indeed fall into the ocean, in was in a treacherous spot.
There are two known cases - in 1989 and 2014 - of people who disappeared, their bodies never recovered, in the sea at Cosy Corner.
In the most recent case, involving novice Irish surfer Stuart Butler, a rescue effort was launched almost immediately and included helicopters and surf lifesaving craft.
His remains have never been found.
The aftermath
The disappearance of Theo Hayez has affected not just his family, but also the Byron Bay community.
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Dozens of locals joined volunteer searches that continued well after police finished their investigation and referred the matter to the coroner in September, 2019.
It was a volunteer who found the only piece of hard physical evidence, Theo's favourite cap, in bushland near Tallow Beach.
Sheri Todd, who helped to coordinate the searches, said the inquest had achieved all that could be expected.
"I think that we are all hoping that there will be an open finding so investigations can continue," Dr Todd said.
"Because obviously we don't have the answers that we need at the moment.
"The Byron community is a very passionate and compassionate community, and I think there was just so much empathy thinking of Theo's mum and dad and brother and all of his family members in Belgium feeling so fearful and being on the other side of the world.
"We'll just continue to liaise with the family and we're here on the ground in Byron, so we can just continue to do whatever they want us to do."
- ABC