Mysteries of missing teen's Byron Bay trip

Theo Hayez was last seen in Byron Bay in May 2019 and his remains have never been found.
Theo Hayez was last seen in Byron Bay in May 2019 and his remains have never been found.

Investigators believe the key to how Belgian teenager Theo Hayez vanished lies with what happened at 1.02am at a northern NSW beach on June 1, 2019.

After midnight, Theo used his phone to swap messages with his stepsister Emma, watch clips from a French quiz show, and joke with a friend on Facebook about an upcoming U2 concert.

But just after 1am, his phone stopped receiving data.

An inquest into the 18-year-old backpacker's disappearance at Byron Bay has heard police believe he clambered up the beachside cliffs, dropped his phone, then fell and was swept out to sea.

His family, who have travelled to Byron Bay from Europe for his two-week inquest in the NSW Coroners Court, don't accept their cautious boy would do something so dangerous in the dark.

They say the only way he would climb the cliffs is if someone was with him, reassuring him it was safe.

Whether Theo encountered anybody else that night is one of the major mysteries the inquest will explore.

Another is how he came to be on the Cosy Corner beach in the dark.

Theo's night began at his hostel, where he shared some 'goon' wine with fellow backpackers before heading into town about 9pm.

At the Cheeky Monkey's bar, the group discussed European politics as they drank a few beers.

CCTV footage played at the inquest shows Theo occasionally stumbling. A security guard who thought he was swaying ejected him about 11pm.

However, the evidence he was actually intoxicated was "ambiguous", counsel assisting the inquest Kirsten Edwards said on Monday.

The decision to kick him out on his own without any chance to tell his friends has caused Theo's family "great distress", Ms Edwards told the inquest.

Theo then looked up directions to his hostel on Google Maps.

His subsequent decisions would be hard to believe if investigators didn't have Google data obtained by his family, Ms Edwards said.

Theo walked in the opposite direction to the route outlined on Google Maps. For seven minutes, he stopped at some cricket nets.

Next he took a dark track through bushland towards the ocean, at points appearing to walk quickly or run.

At the urging of locals and police, coroner Teresa O'Sullivan walked the Milne Track one night last year.

Police have noted it would be strange for a foreigner to walk the frightening and "spooky" track alone at night - giving rise to theories that Theo was with someone else.

He turned off the track into steep, dense bushland and ended up on the beach.

He was at Cosy Corner when he appears to have turned off his location services just after midnight to save battery.

His lighthearted messages sent in the next hour suggested he felt safe, Ms Edwards said.

At 12.55am, he sent a message to his sister.

Then "something happened at 1.02am", Ms Edwards said.

"If we knew what that was, we think we probably would know what happened to Theo."

That's when his phone stopped receiving data.

At 6.17am, it re-entered reception range and continued to receive data until lunchtime that day - indicating it did not fall into the water.

The phone has never been found.

Ms Edwards said the legal team had struggled to get data from Google, Facebook and Telstra to paint a fuller picture of that evening - in particular, whether anyone else was with Theo.

The inquest continues.

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Australian Associated Press